has anyone else experienced skincare products with "xanthan gum" in it causing acne for them? it breaks me out, I'd like to know if other people have the same issue, even at super low concentrations. I can't see anything about it online.

me too. I got acne when I washed it with aveda botanical kinetics purifying gel

In your case, Xanthan is not the culprit. Aveda botanical gel contains Geraniol, Linalool, Citronellol, Eugeno, Limonene. They are the likely reason for your breakouts. Check this