ProSeries and Lacerte are treating the difference between the original cost and proceeds on disposition of an asset that has been fully written off with Section 179 as a reduction of QBI income.  This negative amount is showing on the 199A statement as a 1231 loss.

A 1231 loss is created when you dispose of an asset for less than its book value, and a 1231 gain is created when you sell an asset for more than its original cost.  

An asset with a zero book value cannot generate a 1231 loss.  

In my case, truck bought in a previous year for $30k and fully depreciated with Section 179.  In 2019 the truck was sold for $14k.  This creates a $14k gain, of depreciation (Section 179) recapture.  ProSeries is showing a $16k reduction of QBI income ($30-14=16).  

ProSeries grudgingly opened a Case today, but keeps insisting it is correct.  

The program does not do the same thing with an asset that has been fully written off with depreciation (not Section 179).