I'm submitting this in the hope that it gets fixed even though I suspect that it may be the result of the macOS 12.3.1 update. It actually started happening well before rc8 was released. Last successful backup was on April 30th. Now I can create a new share for time machine backups and the first backup will be successful. Subsequent backups will fail with an error in time machine "Failed to attach using DiskImages2".
Time Machine log-
2022-05-11 22:03:04 Cleared pending cancellat
Solved
Just wanted to say I had this issue on both Intel and M1 Macs. Time Machine backups to Unraid were going swimmingly, with the Unraid share hosting an APFS sparseimage. I'm not sure if it was the Unraid 6.10 update or MacOS 12.3/12.4 or just bad timing, but then all the computers stopped being able to back up a month or so ago. I was able to make first (non-incremental) backups without issue, but subsequent incremental backups after that did not work. I had the same MacOS console issues as mentio