Octamop making only some skin pink.

I have vitiligo, applying octamop lotion(not listing other meds here) to affected areas in hand. while most of spots show no problem post sun exposure, but very few places/spots become dark pink and start itching too. It starts anytime from few hours to next day after sun exposure. Attached 2 pics, one with pink spot one and other with other spots without issue. I just want to know why only some spot/patch have this issue while others are not having issue, though medicine amount and sun exposure both are same to all spots. Please don't give generic response,I want to know really why some spots react with itching/blister/pain while most do not. My doctor is on vacation and hence reaching out for help here to know if it's serious side effect. Need to also decide if i need to stop applying on spots becoming pink/painful. Thank you.