++ Hyper-V Cluster VM backup up - No matching VSS components found for virtual machines ++


we are running a two host based 2012 R2 hyper-v cluster. vRanger (7.8.0) was running for years now.
For some days we cannot backup the virtual maschines anymore. It reults in "No matching VSS components found for virtual machines."
I reinstalled the vRanger agent on the hosts, checked vss writer errors and if service is running (host, backup server and vm), removed mounted integration discs, removed maschines with old integration services from backup and restarted the servers. Current IS is 6.3.9600.19456.

Any suggestions?

Kind regards

Edit 2020/04/28: Last night the backup ran successfully.