There are at least two cases where we run a command against a config server without including a read concern (here and here.

If we don't include the 'majority' read concern, then we'll automatically update our config server optime to the returned 'visible' level, which will not be committed since we didn't query against the committed snapshot.

This could potentially cause future config server operations to hang waiting for the visible optime to become committed, if it never does.