NetworkContexts are extremely heavy weight objects with their own socket pools, their own in-memory (by default) disk cache, which can be quite large, etc.  In general, services should not be creating their own NetworkContexts, because of this.

Almost all consumers should instead re-use an existing NetworkContext (Generally the main one for a profile, or the system one).

Is there a particular reason why CastMirroringServicesHost needs its own?  The minimal configuration makes me think it probably doesn't.