The backup fails with the following error:
The volume ShadowCopy limit for the disk containing this virtual machine's VHDX files has been reached. (Error code 'HYPERVBACKUPCONTROLLER_007')
Clearing the shadow copies of this volume should resolve this issue. Please refer to the knowledge base for further information.
On a particular volume there are more than 100 ShadowCopies, which exceeds the safety limit.
delete shadows all
After the ShadowCopies have been cleared, you can run another backup operation and it should proceed successfully.