The "low" total is due to rounding. I entered amounts with cents (matching the 1095-A I was sent).
In my case TT rounded down, and over 12 payments (columns 12b thru 23b), that amounted to $4 less. In doing the calculation manually, I inserted "Annual Totals" into line 11 of 8962, thus gaining (in my case) $4 on line 24 and line 26. If, when entering data for Form 1095-A, there was a way to just enter the "Annual Totals", I missed it.
If the amounts I entered had been "xxxx.56", TT would have rounded them up, and I would have seen a discrepancy of $8.00 too much (and would have gained that in a refund).
Bottom line: while TT operated "100% accurately", it nonetheless shorted me $4.00. (Fortunately, the actual monthly premiums I paid were just whole dollar amounts and did not suffer from rounding.) Also, when I asked TT to print me a 1095-A, it did not match what was sent to me, because of the rounding. My opinion: there is a programming issue processing 1095-A data entered, that at least needs to be considered.
Additionally: I entered numbers with cents on Schedule B and the cents were displayed in various total lines. Unfortunately, the total amounts were the same, that is, whether rounding the individual items before adding, or rounding the total after adding.