Why do I lose service for 3 hours every night

If you haven’t already, do a whole house reboot. Unplug all stb’s and the gateway. Plug in the gateway and let it fully reboot. Then dvr, full reboot, each stb until all done. If you still get the problem. Unplug all stb’s except the dvr. See what happens over the next few days. If still happening, get a replacement gateway. If still happening after that, get a new dvr. 

Or as @_xyzzy_ said, call for a tech visit to check everything in the house. 

Just to be clear here.   You moved the problem box and now the problem still continued on that same problem box but now in another room tv? The "good" box you moved into your room still has no problem?  If so while I can't imagine what could cause such a thing (some kind of interference that only that one receiver is sensitive to???) when in doubt, replace. 

It would be more interesting if the problem was still on the tv now attached to the "good" receiver now in your room.  That would point to some kind of (very) localized limited range interference (on some kind of timer) in that room.   That could be a harder problem to figure out since it's not a box problem.  I only bring this up to further support that your "yes" answer means that the problem follows only the one box no matter where it is moved to.