During playback for at least 30 mins I notice that sometimes frame rate is degraded to like 12-16 fps. Resolution is to restart Plex app and resume playback. Fast forward, Pause/Play, Stop/Resume operations rarely help. No specific actions during the issue noticed on the network, like updates, NAS problems, router/switch functioning issues.
This is not related to poor NAS or network HW or 4K HEVC. Same happens on 1080p movies with bandwidth under 20Mpbs requirements.