@WDStaff
The by @Keerti_01 provided solution is worthless, as the error is a result of a major firmware bug.
It has already been discribed months ago i.e. in this thread:
I could do backups from all machines without any changes to my Macs, router or other equipment - only by setting the quota for time machine to 100%.
This is a major firmware bug.
WD is selling devices to customers where essential features are broken by a firmware update.
