Pixelated playback when Transcoding for the first 60-90sec

I’m new here, but I’m still having this same issue. I am using the latest Plex version and I have a Qnap 1282-i7 which I stream through a Roku. Actually the problem occurs on all my devices. This problem began about three updates ago and still has not been fixed. Is there a way to go back to a previous update. It’s very annoying.