Sorry, I didn't want to reproduce it because it crashed my computer. I did try to reproduce it now.
I had an old spritesheet 3135x75 that I imported as a spritesheet. When I selected the default size, the one it was offering everything worked perfectly, but when I tried to import it in 209x75 size or any other it crashed again.
Don't worry if it can't be fixed, this isn't so important for me anyways.