Are you still using V2? Many people have been having problems with it since Chrome and Internet Explorer dropped Java support. The new V3 version does not use Java and should work much better for you.
(On the bottom of the page: Click on "Try the new chess.com!")
Under the learn tab, the computer workout has been having problems for some time now. The main issue is that the takeback move is not working. I don't know if it's just me that's experiencing this problem. As of now I can use the computer workout but if I make a mistake I have to restart the entire exercise, since the takeback move option is broken.