You could try the support app.
I'd suggest you do a factory reset and when the phone restarts do not use a back up, start afresh then you are not carrying anything over from a previous backup.
I'd say your phone is faulty then because no one else appears to be having such a large amount of problems as you so clearly it isn't common place, i would use your warranty for replacement or repair.
And yet we have 2 Nokia 8s in our house and both have been absolutely brilliant with the exception the poor low light performance of the camera.
As with all electronic items you are going to get faulty ones and sadly the people that are happy with a device don't post, you only get to see the people having problems and in the grand scheme of things this is only a very small percentage of the overall user base.
I think the biggest disappointment of all Felix (and you have already covered it) is that Nokia don't communicate, it makes it incredibly frustrating for the people with problems, it is like banging your head against a wall.