There is some flaky behavior around creating views during an upgrade process. In the period between when the shards start restarting until mongos has restarted, the cluster may allow you to create a view with $foo (extension stage only available after upgrade) even though you cannot run queries on the view until mongos has upgraded. This behavior is flaky, as it occasionally rejects the view creation to begin with. Note that this only happens when auth is not enabled: when auth is enabled, we have ideal behavior with clear cut upgrade semantics.