Same here - I wrote "The pretty baby doesn't cry much" and it was corrected to "The pretty baby doesn't cry a lot." I reported it as "my answer was right too", because it seems that it should be.
Singular and plural are just about always both right. But sometimes Duo doesn't yet accept both so you have to suggest the missing one.
Except when the Korean ends with 들. In that case it's only plural.
I wrote the pretty child doesn't cry a lot and it was wrong I dont think its fear
Maybe Duo is saying that the only babies he finds pretty are the ones that don't cry much. shrugs