The car: 2006 Subaru Legacy Touring Wagon 2.0 GT (Japanese model) - recently purchased; warranty does not cover this
The situation: Something happens with the 12v supply and once the car is stopped (switched off) dash lights won't come on, central locking won't work, car won't even try to start. No door chimes when key in/door open, etc. Battery OK. Seems to come back after some time. See this video of nothing happening when I turn the key.
Detailed: On Friday I was driving to work and my dashcam shut off, so I pulled over to check it. After checking it was all connected OK (via USB adapter to the 12v socket), I tried to start the engine but nothing happened. Recovery came out and got me started with a jump start pack (although the battery was showing 12v before). On the recovery guy's advice I replaced the battery.
This morning a similar thing happened (dashcam and FM transmitter cycled on and off a couple of times shortly after I started driving), except after ~25-30 minutes of the key in the ignition in the off position, I opened the door and the door chime came on and the dash was once again alive. I turned the key and the engine started immediately. I shut it off, turned it back on, and again it started immediately.
When this happens I can still move my seat (motorised) without issues.
Probably unrelated but: I've currently got a P0410 engine code (secondary air system) showing, which is booked into Subaru for repairs later this month. Hopefully this isn't a red herring for some other electrical system problem.
Also probably unrelated: but I very very regularly get static shocks off the car when leaving it, and when this happens I get a static shock even if I just sat in the car for a minute or two. This could always be the case, since I usually just get in and drive and then experience it upon getting out, but I'll add it here just in case.
The question: What steps can I take next to start diagnosing this? I'm not extremely experienced fixing cars, but I'd like to get a bit more hands on and I do have an electrically knowledgeable friend to help.