Hello Hrish,
You may check if the instances (part of an instance group) have been recreated due to autohealing in the operations log. An operation “Recreate an instance” should be listed with an operation type ”compute.instances.repair.recreateInstance” followed by the “delete an instance” and “ create an instance” ( same instance gets deleted and created ). You may also search the same string “compute.instances.repair.recreateInstance” in the stackdriver logs under “GCE VM instance”. I hope that clarifies the confusion.