Actually, I think that change I made (by logging the 1099-k sale as other income and then again as negative income) created an entry in 8z of schedule 1, which is why my return is now including a Schedule 1. So anyone missing a schedule 1 can use this workaround.
Under other misc income:
add new line item for Form 1099-K Personal Item Sold at a Loss with the value
add a second line entry with the same label but negative value
they will net out on Schedule 1, and the top of your Schedule 1 form will show the correct value.
