Nice to see known people here again… 
Thank you for your helpful responses.
Well, I referred to this:
[1] This Android 9 version appears to sometimes get an invalid WiFi MAC which prevents the phone from using WiFi networks (in the Android mode).
Could you please explain these “couple of reasons”? Reading the posts about 4.3, I’m really unsure if it wouldn’t be better to use 4.2 at the moment and stay with it as long as the problems with 4.3 are (hopefully) solved…
Thank you, peterleinchen. I’m totally aware of loosing camera quality forever once having unlocked the bootloader (sad but true - but even better than being stuck without knowing why)…