So here's my workaround, which is so far working quite well. It's not quite the perfect fix I was hoping for (i.e. full repair -- I never heard back from Ace of Vapes), but it is working quite well and the internals no longer shift under pressure.
As stated earlier, pressure on the top battery terminal was causing the PCB and button to shift, and for the
device not to fire properly due to this. With the battery removed, the internals returned to a much more normal position, without the huge crescent visible inside the button, as well as a firmly clicking button.
I removed the battery and agitated the
device until the button returned to a semi-normal position, where I could hear and feel a satisfying click of the button. I then wrapped a rubber band around the device/button in order to apply pressure to the button to minimize shifting while I was handling it. Using a toothpick, I applied two beads of epoxy: one bead around the outside perimeter of the black plastic disc (affixing it permanently to the battery tube); and another around the outside of the battery terminal (affixing it permanently to the black plastic disc), using care not to cover the terminal itself.
Once the epoxy cured, nothing is shifting anymore, the button fires with a satisfying click. I also compressed the spring in the tailcap slightly to minimize the pressure against the battery terminal.
From the photo you can tell that the button position is still slightly off-center, but I'll take function over aesthetics any day.
The ZMax is once again performing to my satisfaction. Period.
TheSovereign