I'm seeing the same issue. When I ran TT in early January, it did calculate the correct repayment amount (my income is over 400% of the FPL) and so had a $0 repayment limit (meaning I had to repay all the amount shown on line 27. It appears that one of the updates since early January caused this bug.
If you see table 5 in the 2021 Form 8962 instructions, it is clear that if your percentage of the FPL is over 400 you have no repayment limitation (and thus must repay the entire amount of your excess APTC).
