When I login into our Math 112 course as me (a "professor")
I see three buttons for each problem, namely "preview",
"check answers", and "submit". When I log in as a fictional student,
I only see the first two. (However "check answers" behaves like
I would expect "submit" should.) What's going on?
This likely means that your set is "closed" i.e. it is passed the due date for the set. As an instructor you can still submit answers but students cannot submit answers for credit. They can check a given answer but the answer is not recorded.