Here's the broken PCB layout: [https://easyeda.com/editor#id=da34a296559342849c6769dc1b87e409](https://easyeda.com/editor#id=da34a296559342849c6769dc1b87e409) When exporting the gerber files for manufacture, the center ground pads are missing on U13, U14, and U16, but _not_ on U15 - that pad is present, for some reason. This appears to be caused by the ground polygons I have surrounding underneath those chips, but all four chips including U15 have copies of this polygon. Deleting this polygon results in all four pads generating correctly, and for the moment I have replaced them in a different copy with simple traces to link the ground plane through the corners. This is actually a fairly serious problem, as I missed this in my manual check several weeks ago and ended up ordering a set of incorrect boards with the missing pads. My fault, I know, I should have checked harder, but this makes me a lot more wary about using this tool at all, if it's unable to reliably produce correct gerbers.