Without further data, it is very likely that fuel might indeed be the culprit here. You gotta remember, stock tunes leave a lot of headroom, the "hotter" the tune, the less headroom and more ingredient-sensitive your EB ride will become. And if you live in an area with summer/winter gas formulations, all the more important to use the freshest, preferably top tier, fuel with octane rating equivalent to at least that required by the tune.