i hate to be that person that quotes chatgpt, but this seems VERY relevant to your complaint:

“Solar urticaria is a rare condition where the skin reacts to specific wavelengths of light rather than the overall UV intensity. The UV index is a general measure of the total amount of erythema-causing UV radiation (mainly UVB) that can cause sunburn in the average person.

But in solar urticaria, the trigger might be UVA, visible light, or even a narrow band of wavelengths — and the UV index doesn’t capture that nuance.

So it’s not that the forecast is wrong — just that the UV index isn’t designed to reflect the sensitivity profile of solar urticaria.”

In other words, you’re (literally) a special case. :)