MyCloud EX2 Ultra: Time Machine backups keep failing

Hello experts
As same as the topic, my time machine backup became really abnormal since updating to OS5, now my problem is: the backup cannot worked again after the first time backup.

I checked the community then found out that not just only me are facing the time machine issue, I took their advices like reset, system only restore, etc, but my issue still exists.
I need to delete all my backups, then the Time Machine could be backup as the first time, but later it will never able to found backup disk again!!! If I need a new backup , then I need to clean up timemachinebackup folder and roll it over again, totally dead end.

My macOS is 12.2.1, MyCloud OS is 5.20.113. I believed OS5 must have some sorts of bugs, only can wait WD to update their firmware. So frustrating.

See my response here: MyCloudEX2Ultra and TimeMachine (ultimate thread)

You must set time machine size to 100% and use a quota-limited user if you want to limit the backup size.

Thank you andrewtch