Try this:
- Go to Settings → Server_Name → Library
SetGenerate chapter thumbnails=as a scheduled task and when media is added
If it is already set that way, leave it alone.
If you made any changes, selectSave Changes.

- Go to Settings → Server_Name → Scheduled Tasks
Set start time to 0:00
Set stop time to 23:00
Check all same boxes as in the picture
Save changes

- If you have not already done so, make the directories
E:\PlexDanceandF:\PlexDance.
- If
Warcraft: The Beginningis onE:, move it toE:\PlexDance.
IfWarcraft: The Beginningis onF:, move it toF:\PlexDance.
- Perform Plex Dance steps #2, #3, and #4. Perform them in the order listed.
Plex Dance: https://forums.plex.tv/t/the-plex-dance/197064
- Scan Libraries
- Empty Trash
- Clean Bundles
- Return
Warcraft: The Beginningto its original location.
- Scan the library if Plex does not do so automatically.
- Wait.
Leave Plex Media Server running for 48 hours.
Do not power the server off. Do not stop the Plex Media Server processes.
This will give Plex Media Server time to scan your libraries and generate chapter thumbnails.
The CPU utilization may be high during this time. That is normal.