When I go to Folder -> Right Click -> Properties -> Clear Thumbnail Cache instead of clearing the cache you get a message that says, "No thumbnail cache folder has been removed"
I'm using a custom thumbnail folder in my customization config directory. It generate thumbnails fine and the system has full access to the folders.
/mnt/models/thumbnails/mnt/models/Minis/Genre - Named Designer/Cast and Play/36_Dragon Beholder/Beholder Dragon.stl/26500934
-rw-r--r-- 1 www-data www-data 253473 Jul 2 05:03 400_400_contain.png
I ensured the user and group were both www-data for the entire tree and set the permissions to 775
Customer support service by UserEcho