File Backup Error opening file, backup stops

I have issue with backuping files on my UrBackup server.
Everytime server try to backup files, backup stops like in half way and logs say:

Error opening file “/srv/dev-disk-by-uuid-333df066-c281-4fde-8441-32059f15163f/UrbackupMain/place/240911-0724/.b68xO+K9SCOF35cLk4Bf9Q/40” for reading file. File: temp_fn. No such file or directory (code: 2) Target path: “/srv/dev-disk-by-uuid-333df066-c281-4fde-8441-32059f15163f/UrbackupMain/place/240911-0724/Users/H.Kupper/NTUSER.DAT”

Error opening file “/srv/dev-disk-by-uuid-333df066-c281-4fde-8441-32059f15163f/UrbackupMain/place/240911-0724/.b68xO+K9SCOF35cLk4Bf9Q/31641” from pipe for reading ec=2 (this message is repeated like a million times)

FATAL: Backup failed because of disk problems (see previous messages)

My UrBackup server is installed on OpenMediaVault, and backups are set to write on a BTRFS volume with software raid 6. Backups were working 2 weeks ago.