It’s sort of a “clickbait” title I didn’t like myself even if it’s a potentially interesting paper.

Usually we assume dropout helps prevent overfitting, not help with underfitting, but the thing I don’t like about the title is it makes it sound like dropout helps with underfitting in general. It does not and they don’t even claim it does—even by the time you finish reading their Abstract you can tell that they’re only saying dropout has been observed to help with underfitting in certain circumstances when used in certain ways only.

I can come up with low dimensional counter-examples where dropout won’t help you when you’re underfitting, and will necessarily be the cause of the underfitting for example.