Stacked DRBD (DR Node) not Syncing Back to Primary Site

We have following Situation here,

We have 3 nodes with DRBD Setup. 2 Nodes are part of pacemaker clustering and 1 node is DR Node. As part of DR testing we have shutdown 2 Nodes (Pacemaker), and mounted DRBD drive on DR Node. We can see all the data which was there on Primary Site and also we have written new data on DR node. However, after few days, we brought one node on primary site but whatever the data written on DR node was replicated back to primary node.

Replicated back to primary site is automatic or do we need to follow any additional steps

We are using SLES 12.4 Trail Version for this POC

What is your drbd configuration?
Pacemaker is just electing a master (drbd primary) based on the settings you have configured in ‘master-node-max=’, but the real configuration is in the drbd conf.