TJ100,
Unfortunately, one of the experts dug into this and found that the repayment is included in Form 2210 underpayment calculations since as far back as 2016.
If the ACA add-on was the only reason for triggering Form 2210, you can request a waiver based on your specific circumstances, e.g. first time encountered and ignorance of this issue, by checking off the waiver request box and including a statement of circumstances. After all, this is rather obscure and fairly rare for the average taxpayer to encounter. Could be worth a try, IMHO.
