Since all professors are competent, and no competent people are underpaid, therefore no professors are underpaid. Which formal fallacy is committed in the above argument?

The charge is undistributed middle, the term competent failing to tie the other two terms together.

For a valid link the middle term competent must be distributed in at least one premise.

In All professors are competent the middle competent stands as an undistributed predicate.

Unless the middle is properly distributed, professors and underpaid are not truly connected.

Drawing a conclusion across a middle that is not distributed is the undistributed middle fallacy.