SOLVED: Integrated GPU Irregularly Invoked, Playback Issues Result

[Brian]

Thank you for that tip - you were spot on.

My principle client happens to be the Jellyfin Roku app. Going into Settings-->Playback-->Video Codec Support and disabling "Support Direct Play" of both MPEG-2 and MPEG-4 resolved the issue, forcing the involvement of the server GPU during playback, but more to the point resolving the time counter and rewind/fast-forward issues.

I suppose my next stop should be to file a report with the Roku Jellyfin app folk and see what they might have to say.