Ok — you’ve created your SVG and imported it into the app, set the depth of the material, and doubled-checked all the settings. You’re ready to go and you press the button. All is well, until you notice that some the elements aren’t being engraved. The head’s moving, but the laser isn’t firing 
. Is there something wrong with your GF? 
Not necessarily, it could be a PEBKAC event (as in my case). 
The important thing is to stop and think before taking any other action — you may be able to save your print.
While 'forging a piece of slate, I noticed that the lines in the art deco corners weren’t engraving. The finial dots engraved just fine. What gives? I realized that the lines were just that – lines. Vector lines have no thickness, so there’s nothing to engrave. D’oh!
So simple, but how about that print? How can I save my last piece of slate? I knew if I loaded a bitmap (png) version of the corners I’d never get them perfectly aligned to the now-engraved dots, so I decided to “cut” the lines. What the heck — if it fails, I’m only out a $1 piece of slate…
As the file was still open in the GFUI and I hadn’t moved the slate, there were no alignment issues to worry about. I simply switched those elements to cut, and pressed Print…
Sweet, sweet success. 
Btw, as @PrintToLaser pointed out, engraving slate generates a flash that rivals a magnesium flare! Here’s a bit of video as an example. It’s full speed for a few seconds, then shifts to slo-mo.
