My experience of the Mk8 GTI has been very different to yours, Fred.
Since I swapped (rejected) my 2020 (Week 40) Golf GTI for a replacement 2021 (Week 10) and had its software updated from version 1788 to 1803, it's all been plain sailing. I took delivery of the new car on 2 May and have now covered 4,000, almost, fault free miles, and it's been a real pleasure to drive.
I had loads of glitches with my 2020 car but my dealer's response was first class every time, and they offered me a great deal on the swap, when I eventually said I had had enough. The only problem that I have experienced with my current one is that sometimes Alexa won't talk to me for a few minutes..... but I can live with that!
