KHOU switched antennas back in June. It wasn't a big change; if your signal meter only goes up to 5 bars it's doubtful you'd see any change there. But if you were close to the digital "cliff" it could have helped a little.
If it was fine until yesterday, it's probably a temporary situation and will probably be fine again today or tomorrow. I see temporary issues occasionally up here in DFW too. But if not, can you tell us what readings you're getting on the other VHF stations (8 and 13)?
BTW, I can't imagine any reason 11.1 and 11.2 would show different readings. If that persists you should probably rescan.