Hyper-V VSS writer missing

Hello,
I'm using Backup Exec 20.1 to perform daily backups of virtual machines, but quite offten the backup end up failing due to error: 

V-79-57344-37935 - Snapshot Technology: Initialization failure on: "VRTSRV::\\backup.blade.local\Hyper-V?Virtual?Machine\DC_b". Snapshot technology used: Microsoft Volume Shadow Copy Service (VSS).

Snapshot technology error (0xE000942F): Cannot capture a snapshot of the virtual machine volumes. Ensure that the Hyper-V Virtual Machine Management Service is running and the status of the Microsoft Hyper-V VSS writer is Stable.

Check the Windows Event Viewer for details.

When i look for the writer in the "vssadmin list writer" output, the writer is not present there. If I restart Virtual machine management service and run vssadmin again, the writer appears.

Sometimes many backups can complete without the writer dissapearing, but then the writer dissapears again. I can't find any error on warning in Windows Event Viewer.

I'm running Windows server 2016 and the VM's are running on the same server as the Backup Exec is installed on.

So is there any sollution to this problem or a way to find out what is happening to the writer ?

Thanks

Martin