What is an "erroneous judgment of conscience"? 

That term could be--philosophically and theologically--an oxymoron that demeans and degrades the rigors and efforts of authentic "judgment." I think the archbishop seeks and values effortless "conscience conforming," not rigorous judgment.

"Judgment," used correctly by clergy or by laity, should value, not mock, a process of intellectual rigor, study, magesterial teaching, analysis, broad expertise, prayer, education, and experience. 

In Amoris Laetitia, the Pope is saying 3+1 can equal 4; that 6-2 can equal 4; that 1+3 can equal 4....and the media have reported that. Alas, many clergy bemoan that the Pope didn't exclusively hammer:  "2+2=4," and they lament what they see, erroneously, as (with "ambiguity" the new dirty words) "confusion." And as Archbishop Chaput says, "Confusion is of the devil."  

The squirrel might be confused for a moment when it sees snow, but that doesn't make winter or autumn less beautiful--or evil!