I've been chasing inconsistent top layers for a little while when my first layer also started going... very sideways. My printer uses the nozzle to home on a micro switch, which meant that something was probably loose. Initially I was thinking the end stop or carriage, but who would have thought that the printer had shaken the hot end apart over time.
Note to anyone else who runs into this: there is no mechanical stop for those screws and tightening them too far will mash the hot bits into the cold bits. This will cause the hot bits to crimp closed just enough to no longer let filament through. If you find yourself in this situation, find (or buy) a small punch - you can use the taper on a punch to reverse the situation. Don't ask me how I discovered any of this. Why there is no thread lock from the factory, who knows. If anyone reminds me, I'll be sure to let you know how well purple loctite has held up. There's also another screw that goes into the side of the heat break to hold everything in place. That one was loose too.
2.5 hours later: all better!
Lessons learned: multiple, but if you start seeing inconsistent behavior look for a mechanical issue and don't be afraid to tear your printer down.
