One of the corrected final regulations on 199A mentions that:
"The Treasury Department and the IRS decline to address whether deductions for unreimbursed partnership expenses, the interest expense to acquire partnership and S corporation interests, and state and local taxes are attributable to a trade or business as such guidance is beyond the scope of these regulations.
6. Guaranteed Payments" (page 44 on my copy, IV.A.5)
Are you reducing (have you reduced) QBI by the interest expense?