Unfortunately, its always been a mess. Have a look at Cache/PhotoTranscoder Folder Size Sanity Check for additional details.
I personally nuke this cache weekly (been doing it for years) but can also use the prune option from the PlexDBRepair tool → GitHub - ChuckPa/PlexDBRepair: Database repair utility for Plex Media Server databases. However I cannot speak for how well this works on windows (I’m purely a linux person myself).
