The jstests/replsets/reconfig.js does a force reconfig to remove the last node of a 5 node replica set and then calls ReplSetTest.stopSet. If the last node transitions to REMOVED state (because it received a heartbeat with the new config) while we are trying to validate collections on that node inside stopSet, we can run into an error because the node is not in primary or secondary state. Since the test has already finished testing the necessary aspects of reconfig by the end, we can add the node back into the set before stopping the test to avoid this issue.