This is all my opinion, worth what you paid...
We are all early adopters of the Stinger platform, there will be a learning curve. KIA built this performance car designed to be at the performance level that it was released. KIA said "premium recommended", but not required, yet did not require premium. Now the tuners know the buyers of their wares will want the most performance from their offerings, who wants to buy less than max? Every engine has it's own quirks, they are not all perfect clones as much as we want them to be. Tolerances are allowed by design. Parts come from bins. As assembled there will be tight parts and loose parts (due to allowed tolerances). Break in allows many of these parts to wear in, and some engines will have higher output, some lower. This is a fact of mass production, is a good system but not perfect.
Now, we come along and we want to push their design beyond it's release. I know if I buy a hotrod chip (or piggyback) I'm going to push it, gotta see what it will do. So now we are operating our vehicles beyond the design (as released). We are having failures of plugs that are being asked to do more than possible due to the huge gap (but the gap is mostly fine if user is stock and on good 93 premium). I know 99% of the vehicles I've owned that I consider performance have recommended premium, (our premium is 93 here). What if you use non-premium fuel? You probably will be ok, till you push things. Physics dictate things, not KIA. Or regap these plugs to a tighter gap to allow better leeway.
KIA has no desire to make this easy to push their warranteed engines to higher levels, why should they? Added power means added wear. We are going to find weaknesses, the weak links show themselves sooner or later (as we are finding with plugs).
The problems we are having should not be unexpected. There will be some failures in any mechanical piece of equipment, more when pushed. I applaud the companies offering us what we want, but we should realize everything comes at a cost. Failures are part of success. Mistakes happen also. We have a helluva starting platform, just wait if you don't want to have problems. These higher performance parts will take time for us to pick the best, till then we are the guinea pigs. Good luck all, we will get there.
Again, just my .02
