Hyper-V Replica Re-sync after rebuild

[ITGURU]

I have primary hyper-v hosts and then a replica server of the VM. I paused the replication from the primary server whilst I crashed and rebuilt the replica server upgrading its OS.

Once reinstated with the hyper-v role, how I do i resume replication with the existing data on the disks without doing a full sync?

I tried importing the replicaVMs into the console but replication just shows as not applicable and if i try to resume replication it won't carry on?

When rebuilding replicas do you always have to remove the replication, delete all from the replica server, and then re-setup replica sync in full from scratch for each vm?

[Bedders]

I seem to remember that in the past we've done the initial data seed onto our secondary replica by bringing it onsite, then taking it offsite and letting it catch up.

Does it need to to a Resync to establish the baseline again, then a differential to bring it up to date?