What workload is inside that VM? This could be due to many reasons:
It could be because of this reason: https://www.veeam.com/kb1794
In case of SQL it could be because of this reason: https://www.veeam.com/kb1915
And it could also be that one of the writers inside the guest is in a bad state (which mostly can be fixed with a reboot). And there can be tons more reasons for it.
My advice would be to create a support call and log the case ID here (and the follow-up after that) or start with looking at some of our KB's and if that is not the case still log the support call