Print fail-layer gap and strange pattern for top layer?

I had a pair of parts printing overnight, and when they fninished off this morning, one of them had a gap like this in the print:

The second piece that printed next to it didn’t have the gap, which was a little strange. The other thing I noticed was that the top surface wasn’t smooth, but looked like this:

The parallel lines at the bottom are more what I’d expect, and the right side looks normal, but the left has some very strange patterns in it. Zooming it it also looks like the wall ended up thinner than I’d want, so probably need to increase the wall thickness on the part. Any other thoughts on what might be going on here though?

Figured out the gap at least. I got curious and broke it apart at the seam, and there was a full surface in there. Looks like somehow the mesh got messed up. Not visible in luban, but visible in the gcode preview. Also not really obvious in meshmixer, but that could just be not knowing what to look for. The original is fine (this was split), so going back to that to try again, but still not sure about the weird pattern on the surface.