Am I niacinamide reactive, or does BoJ just not agree with me???

I have combination (oily T-zone, dry everything else) extremely sensitive skin. I have both eczema and rosacea for a lovely double whammy, but thankfully no acne.
I live in the mid Atlantic, so humid continental climate, with hot sticky summers and relatively cold dry winters.
Anyway, I recently got into Asian skincare, and I’ve been experimenting with new products. For the most part, they have agreed with me with the exception of the round lab birch juice sunscreen and the Beauty of Joseon rice probiotic sunscreen both of which caused burning and rosacea flares.

I had heard good things about the BoJ glow serum and decided to give it a try, but within a day I was having my worst rosacea flare in years and a full blown allergic reaction on my neck (hives and all.) This is my first time trying a niacinamide product, so I’m trying to figure out whether it’s the niacinamide and reacting to or since I reacted to another BoJ product (the sunscreen) I just need to avoid BoJ for some reason?
This also got me thinking how do you tell if it is a specific ingredient or the brand formulation that is the problem? How do other people with this problem deal? Anyone have thoughts? Advice?