Unclejunebug

I've had stereo gear to replace my entire Bose system for awhile now and have been slowly installing things as time and my three kids will permit. I replaced the Bose HU with a Kenwood awhile back and just recently disconnected the Bose sub from the Bose amp and added an Alpine MRV-M500 and Type R 12" sub in the trunk. The Alpine sub and amp sound great but for some reason when I brake somewhat hard the Alpine amp cuts out completely while all the door speakers continue to play without issue. All the door speakers are still Bose and are running off the Bose amp.

I originally had a similar problem where the amp would cut out randomly but I traced that a +12V remote turn on lead that was loose in the amp terminal. After fixing that issue I can manually jostle the turn on lead without affecting the amp at all, but I'm still left with this strange braking issue. I have the amp wired from the battery with a 4 gauge OFC kit from Knuconceptz and the amp is grounded on a sidewall within the trunk, next to where the scissor jack is located (see pic below). The ground point was sanded down to bare metal first.

On my DVM I see over +14V at the main power terminal of the amp and about +13V to the remote turn on lead, but that's just with the car stationary with the stereo on. Since I can't check voltage while braking my next step is to tape a camera in the trunk and see if the amp is turning off or going into protected mode while I brake.

Has anyone had a similar issue or have any ideas as to what could cause this? And is this a suitable ground location or should I be grounding elsewhere? I've read different opinions about where to ground in the trunk (i.e. strut bolt, spare tire well).

Here is what my current system consists of:
Kenwood HU (grounded behind the stereo)
Alpine Type R 4ohm DVC 12" sub (Wired as a 2ohm load)
Alpine MRV-M500 - 500w @ 2ohm (grounded in the trunk)
Bose amp to power all the existing Bose speakers (Bose amp is grounded to the same location the Kenwood is. Amp ground is beneath the Kenwood ground)
Trip computer is grounded to the Kenwood HU chassis

EDIT: I should note that I have not done a Big 3 upgrade yet and up until this point have not considered one.

Current ground location: