It's basically because you've got mover logging enabled (which FCP warned you about), and the PlexMediaServer share set to use cache: yes. In a nutshell, you're logging every single file that mover moves or tries to move from that share (which at least on my system is around 200,000 files)
Also, generally you would set any docker appdata share to instead be use cache: Prefer to keep the files on the cache drive for performance purposes. (And possibly backup an appropriate appdata share via the appdata backup plugin)
Are all your docker applications using a separate share for their /config mapping? While not a problem in and by itself, generally the way to do things is to keep them all within an appdata share (and separate folders from that), if only for management purposes