I wonder if it's the flavoring doing that, or the increase in PG since most flavors are that way. Although, I could see overflavoring generally causing issues, especially if it's way too high.
We are "mixing" chemicals, and although there is certainly some similarity with DIY, it's good to understand the different chemicals and how they will affect your mix.
You don't have much to lose by trying some lower flavored mixes, if you dislike them it's much easier to bump up the percentages, than try to dilute them.
You may find one shots "harsh" at your flavoring level, but less so if you use a little less for sure. I've been at DIY a while, my tastebuds have returned, it's pretty rare for me to mix over 10% and it's usually much lower.
Best of luck, again,
Anna