All right, I think you are right on the curling upwards. I started another print, which is also using similar hexagonal sides, but is more massive - hexagons are larger, and walls are thicker. And it warps up visibly! When these overhanging arms on upper part of hexagons start printing, they just warp up while cooling. Then when nozzle comes back for the next layer, it hits the warped edges, pushing filament to the sides and making these artifacts. It didn’t break any segments, as they are thicker, but I bet that’s what happened in the original print.

On the new thicker print, the base of the model lifted up from the bed on one side at some point. I was watching the first two layers, so this happened some time later. Gonna try to slow down the print, lower nozzle temp a bit, bump up the bed temp a bit. Will see what happens.