Crashplan eating up TimeMachine backups

I recently upgraded to El Capitan and while checking the system logs I noticed lots of errors about not being able to delete old backups (thin backups), such as:

2016-01-10 05:22:48,193 com.apple.backupd[5904]: Starting post-backup thinning
2016-01-10 05:22:49,319 com.apple.backupd[5904]: Error: Error Domain=NSOSStatusErrorDomain Code=-36 "ioErr: I/O error (bummers)" deleting backup: /Volumes/Time Machine Backups/Backups.backupdb/fünke/2016-01-01-213437
...

and