I had this problem. Tried everything that anyone would suggest. THE SOLUTION I found? the g code line that you choose must be a z axis command. @bar is right it can be tricky because I was using a couple of techniques at once and ended up slicing through my previous work as the machine “knew” where it needed to be but “ignored” the fact that it was passing through material that should’ve never been removed in ALL of the gcode. Patched and painted… all’s well that ends well. Hopefully I have managed to link you to the August subject below. Blessings on your ventures! You’re gonna get it! 
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