Simplify3D User Forum

I recently printed a part for a project I'm working on, and it was quite weak. I dissected it, then saw that quite a few of the infill layers were missing.

It prints two or three infill layers, then create a gap, and starts printing again a few layers before the top solid infill. This causes it to sag badly, and makes it weak.

Here's a picture. After further research, it only skips layers after manually rotating the part. If I import it, place a surface to the bed, and immediately print, it works fine. However, if I manually rotate it 90 degrees on the Z axis, it fails.

Is there some setting that I messed up or is it my bad luck?

Thanks!