After applying a crop to photo (no difference through saving or sending to FTP), 1 pixel black lines may appear in the final photo on the edges (often on the top). I noticed that сhance of meeting this bug increases if you rotating crop frame, using "sharpen" or "fit to box" option.
We checked this bug on:
PM 6.0 build 3889 on Win 10
PM 6.0 build 5378 on MacOs Catalina
both are subject to this bug
Also we tried "edit photo with" function with the same photos that was saved by PM with black border and it's opening in Photoshop without any unwanted black pixels.