The issue was fixed for later version,
please upgrade to E81.30 and it will be fixed.
If you wish to stay on the same version, you can remove self-protection and delete the folder,
it will recreate and after some time it may increase to a big size, the reason it happen is because
the backup load was very high due to huge IO that done on windows server, this cause starvation problem
If you wish we can do zoom and i can assist in deleting the folder but keep in mind it may increase again.
Better option is to upgrade to the last stable version E81.30.