The 50ft HDMI cable raises a red flag. It creates the possibility of a ground loop or spurious electrical interference entering the HDMI circuit that could damage the receiver. The fact that it works fine for 2-3 months and then the issue occurs suggests that some intermittent event or gradual degradation causes the problem to reappear. I would look into using a HDMI balun or some device that will provide a degree of electrical isolation. I would also make sure that the coax cables running from the dish are grounded properly.