Tax Year Prior to 2020: Is there a software bug on Schedule E? Line 24 calculation (simple addition) is incorrect.

No, there's not a bug. Remember the line contains only positive amounts. If you a have negative amount on line 21 it won't be included on line 24. 

Thanks for the reply. I'm still confused.

So here's my line 21 (3 entry columns A, B, and C) numbers: $3,164, $4,919, and $91,910 for three properties--all positive. TurboTax adds these on Line 24 and gets $127,533. Funky math or software bug? ( I get $99,993 using my calculator)

And you pretty sure it's just three properties. The worksheet only show three properties at a time. So, if you have any additional properties they will not be showing on the worksheet itself but included in the sum of the total on line 24. Check and make sure make sure you don't have any additional properties in your schedule E.

Mystery solved! That was it--I have four properties. Thanks so much.