When editing a Late Answer review in responsive design on my Android using Chrome
As you can see, it's pretty much uneditable using portrait mode.
Then, after testing to edit the question without being in the Review queue
Note that this doesn't happen in other communities like Stack Overflow... also to note that in other communities I don't have the same privileges that I have here (not sure if that'd have an impact too).
It could be as well that someone already edited it previously.
