Can't resume synchronization after patch failed on secondary node of Availability Group I applied Service Pack 4 on secondary node of an Availability Group. It failed so I restored the whole VM for the secondary node to an earlier version, and now the data is not synchronizing. 

I have active and passive two nodes. I tried to resume the data movement manually. But it failed. Can you suggest anything here?
When you restored the VM, its LSN was no longer in sync with the primary and thus it can't be resumed. The primary is too far ahead to resume. 

You'll need to drop the secondary and add it to the Availability Group again in order to resume synchronizing. You can do this with an existing FULL backup plus the LOG chain.