A player reported backup failing due to space in the backups path?

https://paste.ubuntu.com/p/M3SmDth4wm/

I think the file that stores a reference to the last backup is somehow corrupted so that it contains only spaces. Tell the person that opened the issue to try deleting the file backups\REDRED\Last.

That fixed it.
Do you know why it happened?

No, I have no idea why that happened. In the next update I'll try to make it so the backup doesn't fail if the last backup file is corrupted, so that'll help.