the s-corp loss is deductible assuming you had basis and it was passive so as to be treated as a passive loss carryover. the QBI for any year can not be negative. negative QBI from an entity is carried forward to offset QBI income in future years. the QBI income in future years does not need to be from the source. TT handled it correctly. QBI is not taxable income. the net QBI is figured and then 20% at most becomes a deduction.
so if the 2018 QBI loss carryforward exceeded the current year QBI income there would be no QBI deduction
also there would be no QBI deduction if your taxable income reduced by qualified dividends and long-term gains exceeded the threshold. look at form 8995or 8995a for the computation.
