The config.system.sessions collection is expected to be a sharded collection spread out among the shards. However, if the user tries to use a session before the collection has been created it is possible for the collection to be implicitly created as unsharded. In this case, it will live only on the config server and when the logical sessions cache refresher shards the collection, the unsharded version on the config server will become inaccessible (along with any sessions inside it).

We should prevent this collection from being created as unsharded and should instead create it as sharded if there is a request to create it implicitly.