I do have Marketplace insurance. I know there was a discontinuity with taxes (when crossing 400% FPL), but my understanding is that it was fixed thru tax year 2025. Maybe there are other impacts I'm not aware of.
What throws me is that it isn't just a discontinuous jump ($2999 to $3000), but that it jumps immediately back to the original trend ($3000 to $3001). I also see discontinuity at $1 (jumps $207), $6000 (drops by $221), $6001 (jumps $222), $8999 (drops $227), $9000 (jumps $228). Aside from these jumps, my refund is perfectly linear with my solo 401(k) contribution up to $10,000 (from the ~30 values I've tried).
