A few weeks ago, Duo started underscoring You used the wrong word errors in weird places, often making it hard to guess what Duo didn't like. I suspect a Duo software update error. (I use the newest Chromium browser + lubuntu 18.04.1 on both computers). Here I mistakenly answered
"Your fridge is empty already", and Duo replied:
"Your fridge is alre ady full." [i.e. misplaced underscore] instead of the expected
"Your fridge is already full."
My italics represent the underscore apparently not available to mere Forum users.