@OreoCookie , tried setting it up yesterday and was successful at first. Then noticed that the cassette wasn’t 100% tight and moving a little side to side, when I pushed on it.
Took it off again and added a spacer on the inside and put it back on - when tightened, the cassette didn’t wiggle anymore, so I was much happier with it. When I sat on the bike to test riding though, the freehub wasn’t working at all anymore and there were some bad noises when I stopped pedaling. 
My very expert assessment now is that I wrecked the freehub body (the pawls and spring came loose, not sure it’s salvageable), but wanted to check whether you were using any spacers or had any other ideas?
As far as I can tell, the Shimano 105 11sp casette that came stock didn’t need any spacers, so I was surprised that the NX Eagle 12sp would need one?