In the migration destination manager, AlternativeClientRegions are used to do writes that don't need to be done under the main op context's session. However, when certain operations are done (specifically those that will wait for write concern), the session from the original operation context still needs to be yielded and so runWithoutSession is called with the original operation context to yield the session, run the command, and reacquire the session.

Reacquiring the session can involve doing a read via dbDirectClient if the session is not found in memory. This will cause an invariant with the sequence of events in the migration destination manager since the opCtx is the original one but the client is from the alternative client region.

This can be fixed by switching back to the original client before calling runWithoutSession.