Yes the flashing lights/needle chase is part of the boot up procedure for the car. When mine was playing up and cut out I got this on recovery.
Car would go black on me, engine would be as if dead and strong deceleration. About 1-2 seconds and it would go through the lights/needles and recover. If I was doing 60-70 I would lose about 20-30 mph in this time and be sitting a touch higher than I was before.
Time to get a serious car electrician on it. Flip the top off the fuse box in the engine bay above your feet roughly. Get another car ofas close to the same vintage as possible to compare to and look for voltage/current changes as well as current when the key is totally out in case you have damaged wire.
My S2 had cabling trapped in the engine bay causing the protective cover to wear and then ground. Constant battery drain and movement leading to shorting.
The Coupe has had bad problems with cabling going through the frame into the door leading to similar issues.
Given the danger this presents to both you and other road users with sudden deceleration risk I would have a polite lawyers letter highlighting loss of trust and potential danger giving them one opportunity to fix prior to return. I have no doubt they will fix it and would not let it put you off but it is best to make certain these things are understood clearly.
These cars are lovely but they do have the ability to frustrate. The more you love them the more it irks. Don't let it kill things, just see it as a burp.
I will admit that when it happened to me it put the fear of god up me and I am glad there was no one on my rear bumper as there often is on our roads.
