I used exiftool.exe on 300 files.
It seems to have done its job.
But... Now, in taskmanager, there is 300x a running exiftool.exe proces!
This must be a bug?
Without know how you did this in the first place, it's not possible to answer this.
Exiftool doesn't create a process for each file it reads and it exits completely once done. Something else is happening on your end.