Now getting bleedin' irritated.
Seat Bolster clip fell off again, door handles sticking again, TCS etc lights still coming on for no reason. getting seriously cheesed off at being a beta tester!
Savage depreciation as well!
Praise the lord i didn't buy on a pcp or I'd be up the swannee without a paddle/
Your Christmas lights sounds like a line of code is missing from the The ECU, I suspect that there will be a software update that will cure your problem. The question is why the dealer has not addressed the problem when the car was in for its second service.
The issue should be dealt with under warranty does not matter what the fault is if you have kept up the service protocol then a fault such your Christmas tree lights should be dealt with by the dealer and paid for by the maker. The old goods not fit for purpose line should move them into action. Even drop the chief exec a letter you might be surprised how quickly they sort out your problem.
Best of luck