I have a small jigsaw-shaped modular tool holder that I printed recently on a plate of twelve (two rows of six).
Inexplicably, two of the objects have different top layer solid patterns from the rest as can be seen here:
The plate is generated via a simply for() loop in OpenSCAD and there is no Z offset difference across any of the objects.
I print at 0.2mm layer height with 0.5mm extrusion width (0.4mm nozzle) - with 2 perimeters and 5 horizontal shells. Infill is rectilinear at 20% and solid shells are NOT concentric (as can be seen in the other objects). Weird, huh?
I'm not looking for a solution to this by the way - I just thought I'd share it as I've only just noticed it (I'm also still using v0.9.9 so later releases may have fixed this).