Offline backup

Hi,

we have BE 21 on a server 2019 and since last week we haveing problem with backing up somoe of our Hyper-v VM that are server 2012 R2.

it look like that when some of the server 2012 R2 get backup server goes in the pause status and we see this error for the server:

V-79-57344-38769 - Virtual machine 'servername was backed up using an offline backup, therefore the VHD / VHDX files are only crash consistent. File-level recovery can be performed, but results may be unpredictable. Application-level recovery cannot be performed for this virtual machine.

Why BE suddenly try to backup this VM offline? I did run the  vssadmin list writers on the server and no error there also all the services on the VM is running and there is enough space on the C drive on the VM server!

any suggetion?

Thanks