I have a Nickel "sensitivity" in vaping, and a Nickel "intolerance" per food.
So, this is something that I know a little bit about (just on the level of personal experience).
What I've read most often is that a Nickel sensitivity per vaping is most frequently associated with sore throat type symptoms. Most folks stop using Nichrome wire with this discomfort, and so it's hard to say what other symptoms may result from prolonged use (see ↓ "food" symptoms)
Yes, the 10-14% Nickel in SS (300 series alloys) is plenty enough to cause a reaction.
Kanthal, however, should cause absolutely no problems. So, if you're pretty sure you're reacting to Kanthal as well, then most likely not a Nickel-related problem.
I vape SS 430, and can vape Kanthal (but don't, because it seems to crud up much more quickly with nic salts).
FYI & BTW, a Nickel "intolerance" (per food) often results in skin issues (itchy, rashy, "eczema" type stuff, and itchy zitty face type-style stuff too betimes).