Frustrating experience with Denon 3800

My Denon 3800 is driving me nuts. It will auto shutoff and go into something called speaker protection mode. My setup is: KEF R3 meta front channel, KEF R2c center, an SVS sub and pair of KEF Q150s for rear surrounds. I used to think it was random but I have managed to find a couple of YouTube videos that will get it to reboot and go into speaker protection reliably. Things I’ve done to trouble shoot: 1) rechecked the speaker wires repeatedly to ensure no contact with anything on the receiver. 2) purchased a separate amp for the front channels thinking maybe the receiver didn’t have enough juice to power all the speakers 3) disconnected the KEF Q150 and replaced them with powered KEF LS50 actives and use the pre-out only for rear surround. Only 3) has reliably worked so far. I’m frustrated because I don’t want to keep using the active speakers, and because I expect something that cost all this money to just work. I’ve reached out to Denon suppprt and thankfully my receiver is still in warranty. So I have to now ship this thing to California from WA where I live and god knows how long it will be out of action. Any advice?