Need help with New system! 2 sundown x12 4th order

[Jaydm919]

This is my first post but I've always searched on this forum for any help.  I just finished my first real system.  I have a 2015 Honda Accord Coupe with 2 Sundown x12 d4 in a custom made 4th order that a good builder made for me. Wired at 1 ohm using a Twisted Sounds 2.8k amp, running a limitless 40ah lithium battery. I just got my car back yesterday from getting the box built, its a 7 cubic feet box tuned and built for my car and subs. Its very loud but after playing the subs for a little half way i turned it up a little more just 3/4 and the bass cut out but can still hear it thumping just no low bass.  Its hard to explain but after it did that the bass just sounds like waves of bass coming in and out and doesnt sound clean. The gains were set with a DD1. I started the car again and it played fine but without even turning it up 1/2 way the bass did it again. It still plays but just thumps and in and out clean bass. I checked all my wires and everything is connected and fine. I turned the gain down a little and it still did it. The amp is mounted in the trunk on the box while the port faces inside the cabin. The box flexes but not much could something be damaged in the amp? it never did this before.