FFS deletes files on left side while using Mirror

[max23232323233]

I want to mirror my files to a backup drive, now FFS wants to delete a file from the original drives (left side).
Why?

Image: https://ibb.co/Rj2sPM7

[xCSxXenon]

Click the green cog and show us your sync settings, they are wrong.
Get an image of the global settings and the three individual local settings