So, the Radpower guys really responded immediately and promised to replace both the wheel and the fork ASAP. Thumbs up guys - another gold star from me. If it hadn't been for the responses I've gotten from Ty and Mike, my feelings for this adventure would've been a lot different.
Luckily the guy at the e-bike shop managed to fix the problem for now (it cost me 100 USD - hoping to get those back). Here's what he wrote to RP for me:
"The wheel loosening was caused by faulty installation. The wheel was initially fastened too low in the dropout. The cause is hard to pinpoint. Most likely the "Torque washers" have been installed up into the dropout - or the installation may just have been wrong.
To alleviate the problem I used a file to fix the interface between frame and motor inner nut. A picture is attached, but the quality turned out worse than expected. The dropout was also filed lighly to fix previous damage from the loose axle. Then I installed a Grin Tech Torque arm rev 4. The motor axle is noticiably undersized. It should be close to 10mm, but measure in between 9,4-9,5mm."
And here's a picture of before and after:
I've now been on my first real test ride and everything seemed ok. I'm gonna tighten the nuts pretty often in the weeks to come, just to be sure. This should come as a warning to you, to be careful on your first runs with the bike, even though I think what happened to my bike was really rare.
But the bike is AWESOME!!! I cannot believe the smoothness of the ride and the power of it. I almost feel ashamed, racing by everyone else. I'm a typical Norwegian in the way that we don't like to stand out too much in public, but this bike will get (also unwanted) attention if I ride it too fast around the city. It's not really street legal, and now I know why.
To put it in level 5 is just ridicolous and not necessary, even here in this city, full of hills as it is. And I love using the throttle to set off and get some extra speed downhill. Doing it uphill was so fun I cannot believe it (and it's illegal - so I got to be a little careful). I've set the max speed to 29 kph, which is within what is legal and I think that is more than enough. The important thing is the power of it.
But the most practical fun of it all is how the bumps in the road just disappears with these tires. I already feel like I cannot go back to ordinary tires again. This was also the factor that made me buy the RR in the first place.
Now I have to dry my back, because it was wet and cold outside and the fenders are still waiting to be installed.
And oh, the motor? It's so quiet!