I have two Roku devices -- a Model 4630X Premiere + and a Model 4200X. The 4630X is running OS V 7.7.0 Build 4108-29. The 4200X is running OS V 7.7.0 Build 4108-04. Both are the latest updates as of this writing. One unit is attached to my 4K HDTV in the living room, and the other unit is attached to a 4K HDTV in the bedroom. As other users have indicated, Netflix will stream fine for 20 or 30 minutes, and then it will pop out of Netflix and revert to the Roku Home Screen. I tried deleting the Netflix channel, rebooting, reinstalling the Netflix channel, and this behavior persisted. This bad behavior began with the last or last couple of OS update(s). Prior to that, the Netflix app worked fine.
Also, on my 4630X Premiere +, the update to OS 7.7.0 Build 4108-29 apparently broke my Slacker Radio app. The Slacker app fires up OK, logs in OK and allows me to select a music channel. It then begins streaming audio but quits after about 10 seconds. If I skip to the next song, it will stream audio again for a few seconds and quit. I've also deleted this channel, rebooted the Roku, and re-added the Slacker channel with no change in behavior. Slacker worked fine on the Premiere + until this latest OS update. However, Slacker still works fine with the latest OS update on my older Roku 4200X.
Both of my 4K HDTV's are "smart" TV's with an internal Netflix app. Netflix works fine on each one. Neither TV has the ability to stream Slacker Radio, however. My ISP is Spectrum, and I get a very reliable 118 MB/sec on downloads and 12 MB/sec on uploads. So these issues are not constrained by my ISP.
Anyway, I just wanted to add my 2 cents to the discussion that the latest Roku OS updates are breaking apps.