Were these items already previously added to your server?
Or was, or is the same folder also added to a second Plex library?
If you cannot rule this out, I recommend you to perform the Plex Dance with these items.
However, doing so will reset their ‘Added at’ date in Plex.
The only other option I can think of is to ‘unmatch’ them all.
You can see what’s inside of this file in your first screenshot above: HEVC video with a very weird framerate of 22.742 fps.
Transcoding HEVC requires a substantial amount of CPU power, unless your device has a dedicated hardware transcoder with support for HEVC.
The non-standard framerate will no doubt contribute to the jerky behaviour.
