First you manually prepare Form 8978, Lacerte doesn't do that. Looks like when the adjustment favors the taxpayer inputting a negative number in Screen 45.3 causes it to carry to Schedule 3 Line 6.  If you owe additional tax,  enter a positive number. Lacerte adds this to the total tax and increases Form 1040 Line 16.  Either way you get a diagnostic saying it can't be efiled, even after attaching the Form 8978.