Turn off "Auto Adjust Display Refresh Rate" under:

Settings > System > Advanced System Settings > Advanced Display Settings

It even says (in the description) that it could cause flickering! Seriously, ROKU?

I left HDR subsampling at 4:2:2 (doesn't matter if you choose 4:2:0, instead)

Hope that helps! This was driving me up the wall!!!

I did turn off Auto-adjust Display Refresh Rate a while back. It made no difference with the screen flashing black. It still goes black regularly.

Did the cord cutting and purchased the Roku Premiere approx. 6 months ago for 2 y.o. Samsung smart TV.  Worked great.  Then the black flashing screen began.  
Even the screensaver was flashing black.  I knew it wasn't the TV because after switching to OTA the blinking disappeared.
Next day ran out (and blew another $99) purchased the Roku Ultra, assuming the Premiere crapped out.........  One day later, flashing black screen.

Come on Roku.  Some help for us pleeeze.......Really dropping the  ball here. 
Been a fan of your products since the beginning.....ready to bail out to another platform. 
A sad day when my cheap antenna gives me a better viewing experience than the Roku box, not to mention all the time I invested setting up apps, emails and passwords.  UGH.

I bought the Ultra back in November however just started using it with my Sony 900E. I have a Pioneer VSX-1311 that does the HDMI switching, along with the Roku, I have a XBOX One X attached to the TV this way as well. I have yet to have any issues with 4K 60fps / HDR10 signals with the XBOX, however the Roku starts flickering (displaying a black screen on and off) usually after watching a 4K video. I have the latest firmware and had already upgraded all my HDMI cables to Monoprice certified premium 18Gbps versions but just for testing purposes tried other HDMI cables on the Roku as well (Amazon Basics High Speed 18Gbps, ones that came with the XBOX One X, Twisted Veins) all cables connecting the Roku have been 6ft or less. The only way I was able to stop the Roku flickering was by setting it to use 4.2.0 instead of 4.2.2. So far this has worked, I've been able to watch YouTube 4K/HDR videos and return to the home screen without the flickering happening. I'll update if the flickering starts again but would be great if a ROKU service rep chimed in and mentioned other possible causes of this flickering (besides repeating the change HDMI cables, update firmware comment).

Just wanted to put my vote on. My ultra flickers black. I know it's not the TV because if I'm watching anything with commercials, it switches to that with video. It pauses the audio when it flikers. It just started a few months ago. Also I've noticed that it gets hot as crap when sitting. It's on a bench with plenty of air flow and even put it on a stand since the vents are on the bottom. I hope they fix the issue soon.

I've been having Roku Ultra blanking problems for a year. I've tried ever possible permutation of settings with no improvement. I also purchased 18Gb/sec HDMC2.2 certified cables from three vendors and used them. No improvement.
Today, I finally solved the problem, but it took a$120.00 investment in a Monster Cable Ultimate 27Gb/sec HDMI cable with a lifetime replacement warranty to eliminate obsolescence

The problem is that in 4k 60 Hz OR 30 Hz mode on a 4k Samsung TV, the handshake between the Roku unit and the TV is being corrupted, or the protocol Samsung (and that which others are following) is varying from what Roku demands. 4k Roku devices are not forgiving when it comes to cabling. 18Gb/sec HDMI 2.0/HDMC2.2 certified cables should be sufficient, but they clearly are NOT. I have even had random frequent blanking at the 2k level. In the case of Samsung, Roku tech support does not understand the Samsung Smart Hub requirement as the only source of HDMI/75 Ohm coax inputs. Many tier 1 techs (mostly outsourced from southern India) have no idea that the Smart Hub is fundamental to the very functioning of the Samsung TVs. Without the Smart Hub and it's proprietary cable, you have no inputs. The techs even told me to eliminate the Smart Hub!!!! If I did, I'd turn the TV into a bulky, expensive paperweight!! Roku needs to do a better job in-servicing their customer support, and Roku agents need to stop telling Samsung TV owners to change the advance display settings. These settings allow you to reduce the amount of chroma data relative to luma data....by reducing 4.2.2 to 4.2.0. Do NOT do that! That is not where the problem lies!
You will be unnecessarily reducing the picture quality.
I have had my year-old Roku Ultra on all day long with the 27 GB/sec cable and not even one blanking episode....not one!
And I've been having them 20x per hour from 2-8 seconds in duration, many times ending in the "purple screen of HDMC violation warning death." My problems are now solved.

Why did this happen?
I believe that the existence of the mandatory Smart Hub, a stupid engineering idea by Samsung, relegated the delicate HDMI signal to an unnecessarily long cable and there is invariably some degradation of signal strength. A borderline cable (18Gb/sec) leaves you wide open to packet loss or data corruption, degrading the TV-Roku "handshake." The Digital Rights Management restrictions placed upon your Roku device and your TV are STRICT. If your signal is weakened or degraded, you'll get an HDMC 2.2 protocol warning again and again when blanking gets out of control. You can thank Al Gore for his "work" on DRM in the 1980s-90s to prevent audio and video piracy (sarcasm). If DRM didn't exist, we wouldn't be having this problem. But just like Macrovision wrecked VHS videos in the 80s and 90s, HDMC anti-piracy issues today are making Samsung engineering sloppiness more of a problem for us with our Roku devices.
I hope I have illuminated the problem at hand. To paraphrase Bill Clinton, " it's the cables, stupid."
You can purchase 27Gb/sec Monster HDMI Ultimate cables from Amazon and likely say goodbye to miserable blanking
Good luck!

Just got a Roku Ultra 2 weeks ago, and I noticed these 2-3 second black screens every 30 minutes or so happening on every channel and even on the main screen.
My TV is 1080p only, HDMI 1.4, so a lot of what is written here as the "source of the problem" being some 4k stuff doesn't apply, yet it still happens.
I've changed inputs, HDMI cables, all the suggested settings, and also Roku units (returned one and got another one) and I've gotten the same result every time.
It is very annoying since my old Roku stick does not have this issue and performs perfectly with my TV. (Samsung UN55FH6030)
The reason I got a Roku Ultra is to get 5.1 audio, but if the trade off is to get random black screens, then I'll return my unit and find some alternative.
I really like the Roku system, but I'm afraid of what I'm reading here and in other forums regarding this problem and how there is no support or even if Roku will do anything about this issue.
And changing my TV is obviously not an option.
Help please?

beegee wrote:

Come on Roku.  Some help for us pleeeze.......Really dropping the  ball here. 
Been a fan of your products since the beginning.....ready to bail out to another platform. 

The problem is, what platform? I'm all ears. Apple TV, Chromecast and FireTV are all weak by comparison. I really wanted to like FireTV but it's WiFi only and can barely handle presenting 1080p content without stutters let alone 4k content. Plus its OVERLOADED with unwanted, unavoidable, distracting advertising. I could by a Playstation 4, but I don't play console games so that seems like major overkill and waste of hardware and it lacks a number of apps from the Roku. Same for an Xbox One.The only one that might be viable is an Nvidia Shield at $179 or $199 or basically twice the price.
Amazingly Roku wins nearly every head-to-head comparison review even with these issues which suggests we're just in a LOUSY period for these devices right now awaiting a new knight in shining armor to come riding into the story.

I've just started seeing green lines on the bottom part of my screen while in roku. Yes, I'm running a Samsung 4k uhd TV. But every other device I own (shield, Apple tv, ps4) doesn't do the blinking black screen or the green lines. I swapped HDMI ports and cables to make sure it wasn't the TV. This sucks cause I loved the roku.. But I guess I'm going to have to switch to one of the other devices. I really hope they get this fixed. I'm sure it will be a simple fix (on their end).

 Black Screen Resolved: I have had Roku models 1, 2, and 3 over the years. They were all pretty much set it and enjoy.
After purchasing a Samsung 4K UTV, I wanted to keep all the channels not on the Smart TV.
Unlike my experience with other models, the Roku Ultra has had three performance problems in the two months I've owned it.

1. Dialog (voice) not in sync with video. Solution: Set Audio to Stereo.
2. Static bursts in sound at times. Solution: Corrected itself, possibly from updates?
3. Video screen has interval momentary Black Screen. Solution: Under Advanced Settings, changed Refresh Rate to OFF.

The above problems have been very frustrating after many years of enjoying trouble-free Roku TV.
I hope the solutions I found work for you as well.

nightwatcher2017 wrote:

1. Dialog (voice) not in sync with video. Solution: Set Audio to Stereo.
2. Static bursts in sound at times. Solution: Corrected itself, possibly from updates?
3. Video screen has interval momentary Black Screen. Solution: Under Advanced Settings, changed Refresh Rate to OFF.

Setting Audio to Stereo is a horrid solution for those of us with surround sound setups that want to enjoy it. It means our one $90 device is negating a MUCH higher investment in other equipment.
The Refresh Rate setting is part of the whole new feature set that was supposed to represent a huge step forward. Instead its been several steps backward.

I NEVER ONCE had a problem with my Roku 3 blanking on my Samsung @ 1080. But it started when I upgraded to a Roku Premier+. Tried everything. They even sent me a new one. I even got a new HDMI cable, but the black screen only happens on 1080. It never happens with 720.

My unit does this too no matter what source I use (Hulu, Amazon, Plex). At first I thought it was a loose cable or maybe a heating issue, but it continually does it until I shut down the unit and unplug it (restarting sometimes helps).  I am so disappointed in the performance of this device (Ultra and Premiere) that I will probably not buy another Roku unit.  Amazon's fire TV (3rd Gen) is now just as cheap.

I still have (perhaps delusional) hope that Roku will get this right, but the experiences for so many have been a mess since the solid performance days of the v3 units. Everything past that has been a compromised experience. So, I finally took some action and tried out the Nvidia Shield TV in my theater and it's been night and day. The shield, while costing twice as much, does twice as much and does it faster (sometimes shockingly faster) and with near total reliability. At least now I have a solution to, at a minimum, ride out the tide until Roku gets their act together. The question by then is, will I even care? 

This is the worst of all cases for Roku as a company and it's a totally self-inflicted wound.