pinglis wrote:

plex roku app is experiencing the server not fast enough,
However all movies and tv series play perfectly on the fire stick app and also while using emby .
everything played perfectly until about a week ago

any suggestions?

That's really a question for the Plex forum, and I believe you've already posted there. It could be a setting on either the server or app. I believe you can force direct play on a video and see if that resolves your issue. It's possible Plex is transcoding the file when not necessary, since the Fire can play it.

I have seen this too and it is starting to peeve me because I see it on my Roku TV and my express and older HD do not exhibit this behaviour on the same video -- all 3 set to direct play

I have not seen any problem like this at all. 

Just guessing I do think that it may be related to server problems but those problems, if they are real, do not exist for me.

Two things to try that may or may not help:
1. Reboot the server. This is particularly helpful if the server has not been rebooted in a while.
2. Optimize the Plex data base. on the server main screen right click on the three dots next to the word "Libraries" and then choose "optimize" from the drop down menu. This is mainly a fix for slow navigation but it can effect streaming as well.
 
Another issue is if your clients are connected wirelessly. It could be that wireless interference or some such has reared its ugly head. Of course the server should NEVER be connected to your network via a wireless connection. Wireless is just to unstable to be reliable as a server.