612 receivers are much more "buggy" in my opinion than your other dual tuner.
1. It's in a pole barn? We've been getting some rather warm weather lately so make sure it isn't getting too hot and make sure it has plenty of ventilation around it for air circulation. If you suspect it could be getting too warm but airflow is not restricted get a fan even and aim it at the receiver.
2. As crazy as it sounds I've had a lot of issues fixed by adding a 3 prong adapter to the electrical cord. I'm talking about the kind of adapter you would use if you had older wiring that didn't have the electrical outlets with 3 prongs and had to convert it to two prongs. Even if it's a grounded new outlet, add one of those adapters.
Definitely try the 3 prong adapter trick.
Good luck!