I was having a similar issue. I checked every wire from the battery to stereo to amp, checked the ground, pulled the stereo to double check the wiring was all correct. Everything seemed good so I thought it had to be my battery not putting out enough power. Tested it and it was good. What it turned out to be was the connection from the power cord to the battery. It had a tiny bit of built up corrosion that was making the amp go into protect mode. Cleaned it up and hooked it back up and has been golden since.
The link attached is pretty straight up on what you need to check for different circumstances. I'm guessing it's a low voltage issue. Good luck