To prevent issues with ngons, you can add a Triangulate modifier on the top of each modifier stack. After you apply the boolean modifier, remove the remaining triangulate modifier
Just found another way too. Just triangulate the problem part (which has no ngons!?)
Any idea why? The nGons on the sprue were just a quick way to fill the open
ends. I was planning on triangulating as I exported the STL. After all the boolean
‘generates’ ngons, it shouldn’t be averse to them.
Thanks Richard. I can at least get moving again on this.
But it’s not the quad fan (at least not directly). I think it was just the change in
topology or face count. Other parts had (and still have) the same structure and
caused no problems. Go figure.