I just logged in because I have been seeing this same issue for a couple of months, and wanted to see if it had been reported yet.
They just updated the plex server to support header compression (which I believe the roku developer said was the issue).
“Just updated” as in which version? Has this been released yet? I have the latest Plex Pass version (184.108.40.20695) and I am still seeing the problem. I tried changing the transcode setting to HLS, as recommended, and it didn’t make any difference for me. I can confirm that disabling Direct Play is a viable workaround.
I can also confirm that removing header compression fixes the problem. It seems as though releases of
mkvmerge between 4.1.0 and 6.0.0 had header compression enabled by default, but that it has been disabled by default in more recent versions. This would explain why only a smattering of files in my library exhibit the problem. Since it’s disabled by default in recent releases, removing compression is as easy as:
mkvmerge input.mkv -o output.mkv
This command takes just seconds on a full size movie on my system, and even if / when this is fixed, it’s probably a good thing to remove header compression since it can cause playback problems on other devices as well.