The code to recover access blocker for shard split (https://github.com/10gen/mongo/blob/af171a2a74353693ce811a55577c1aa86ae2cdb4/src/mongo/db/repl/tenant_migration_access_blocker_util.cpp#L600) at the end of a rollback or initial sync install one blocker per tenant. The shard split observer expects one blocker shared by all tenant and will not correctly deal with the access blockers.

This will be fixed in master by SERVER-75237 but we need to fix this in 7.0.