@David the swarfer, I have a weird thing happen. I uploaded a .dfx from Fusion 360. I phlatedged it. I made a center point in all the circles that were supposed to be drilled and generated the file. To my surprise all the holes are doubled with one hole at the proper place and another at a bit radius offset. When I erase the circle but leave everything else untouched, the holes are generated correctly, only one hole at the correct place. You can see in the image that the upper left 4 holes are OK, the circle was erased, but the other ones are double. It's not a biggie, I can work around it but I thought I'll ask you if you can find what I did to cause it.
I know exactly what causes it, and the only way to prevent it is to not allow anything to intersect the purple line from the center of the plunge hole to the edge. Recent versions of SketchUcam create the plunge hole as a group, which sometimes prevents the double drilling, and sometimes does not, the only sure fix is not having any lines crossing the plungehole colored line. The fundamental issue is that Sketchup allows all lines to intersect all other lines, even groups, even hidden, and even lines on different layers. This means that any intersection within that purple line is seen as 2 lines, with a plunge at the start co-ordinate of both of them.
