It's gotta be in the tune, I'm running UM tune on stock plugs, with mods in my sig at 30 psi spike on their adjustable file, it basically lives in the 27-28 psi at wot and have never had misfires or limp mode or any check engine light since modded which was since new in 8,000 miles. I've also got a 16 running UM tune 29 psi spike, drop in filter only, stock plugs which also has never experienced any issue, they're both 93 oct tunes, we have up to 10% ethanol added in our pump gas, these cars have run on tunes since new on winter and summer blend gas on stock plugs with, it looks like, more aggressive tunes on stock plugs without any issues at all.
It's funny how many companies blame the plugs or gas quality immediately, don't get me wrong it makes sense, unless there are this many people experiencing the same thing all over, seems like the common denominator is the tune.
While I agree it's smart, for piece of mind to regap and run a lower range spark plug, it shouldn't be necessary. I'm swapping in those stupid expensive ngk race plugs, but only really to check the stockers and give these high dollar plugs a try, I do plan on changing plugs every 10,000 miles personally as that's just my maintenance preference but not cause I had to, to attempt to clear up any issue.
Sucks you guys are having this issue, really sucks the lack of support it seems you're receiving from your tuning company. Just thought I'd chime in as an example(s) from a different tuning company. Good luck guys and ladies, hope it gets sorted out for ya all!