Nothing outside of what is reported in box 20 of a Schedule K-1 (Form 1065) has any effect on UBTI. UBTI is the amount reported with code V in box 20.
As far as I can tell, a partnership cannot report an amount less than zero for UBTI. Section 512(a)(6) says that UBTI for each separate business is to be calculated separately and the UBTI of each separate business shall not be less than zero. https://www.law.cornell.edu/uscode/text/26/512
Do you have Schedules K-1 (Form 1065) reporting negative amounts with code V in box 20?
