I am getting this error on a backup and the file that is causing the error is giving this error: Sequence contains more than one matching element. What does this mean?
It's a known problem when using hybrid plans caused by files with the same modification date. Should be fixed in June. As a workaround you can use 2 separate plans instead of a hybrid one.
Might have a fix for your problem, so if you want to test it out send us diagnostic logs via tools > diagnostic menu mentioning this thread in the issue description.