Not sure if this is anyone's issue here, but I was seeing somewhat similar behavior where MC would see a networked HD Homerun tuner for a while, and then fail to detect it, and restarts would fix it sometimes and not other times, and it seemed to disappear at random. The cause, in my case, was disabling the DLNA controller option under media network on my server box. Once I rechecked that box the tuner was never "lost" again, and with the box unchecked I only "saw" the tuner sometimes, it was very erratic.
I'm not sure why it worked at all with the box unchecked (even sporadically), but I thought I'd offer that as a troubleshooting point because it eluded me for weeks, and was an easy fix.