[Update - I see the 4/15 update fixed properly, so ignore this workaround]
FWIW, I had similar situation where my excess ATPC is auto-added to medical worksheet as a deductible expense. I did Itemize, but without paying back excess ATPC, actual medical expenses were below 7.5% threshold.
Here's what I did to successfully efile and have it accepted.
For the last question "List any expense refunded" in the Step-by-Step on Medical Expenses, I put in the number that matched the excess APTC that was forgiven. (The question said "reimbursed by insurance", but I felt the reimbursement by the IRS was close enough, and the math nets properly.
Also, the Medical Worksheet isn't filed with IRS, it's just used to fill Schedule A, which now has my legit value. Schedule A is the form that is sent to IRS. [I looked at Schedule A, to confirm it was clean and accurate.]
The worksheet has the slightly clerically imprecision of adding ATPC and subtracting it in the other line. Doing it that way in Step-by-Step, avoided a manual form override that might have had ripples I didn't understand.
YMMV, but it seemed to be a clean workaround for me.
