I think 90% that the shorts are caused by issues with the 510 insulator.
The 510 installed is meant to be used with an atty O-ring, like the one that’s included in the bag. That means one should place the O-ring underneath the atty before attaching the atty, to form a seal. Perhaps some people did not use the O-ring? I always thought the O-ring is required to prevent leaks, and I’ve always used one. But anyway, if you did not use the O-ring and screwed down the atty very tight then it might shear the insulator. That’s what happened to Walter Ego, given his posted pics. With the O-ring, there should be about a 0.5mm-0.8mm gap between the mod and the atty.
If you do not use an O-ring and you screw down atty such that there is no gap between the atty and the mod, then you should use the deeper 510.
My advise: don’t screw down the atty too hard before test firing. If you’ve already ruined the fuse then please check the 510 insulator and replace it if necessary. This should prevent you from blowing more fuses.
I included two 510s precisely because of lack of an atty standard (some has center post that protrudes out more than others), and different ways people screw on the atty. With the two 510s and different O-ring thickness choices, the mod should be able to fit just about any atty any way people want. At least, that was my intention.