Thanks @BrutalBirdie for the fix!
@brutalbirdie thanks, I merged it and made a new package release.
@fbartels it works, thanks!
I now tried a single app backup with the lock file in place and no problem.
I will now enable auto backup for this app again and see if the full system backup gets stuck again.
scratches had 😕
@christophermag This should be fixed now.