@Dezerd you just have to start-copy the Replica VM it permits the original job to keep replicating on the VM. there is no failover/failback mecanism AFAIK if you work on replica started VM, you will have to put up in place a replica going to original hosts

For information : The downgrade change nothing. The only solution was to reinstall xcp with the upgrade option (even if it was up to date before the bios update) If we go back to the original problem, the latest version of the Bios changes nothing (there is no information about the BIOS on the Host page)