does anybody knows, if this is critical?
The task has finished successfully, but: old Agent Incremental Backup Backup "X:\Backup-M-ab-2017-08\M-SRV02\backup-version-2018-01-07-140333" is not consistent, please check log file.
Re: not consistent
Potentially - my experience has been that when this occurs vm explorer will initiate a full backup. This happens in my environment when I perform a restore or when a VM is removed and a replacement VM is built with the same name.
I say potentially because if your retention keeps a specific amount of full backups then an event like this could unexpectedly reduce your retention window.