I'm getting this problem too, using IE. Usually the ones it sticks on are one where I won! Only happens occasionally but very annoying.
Using Chrome, the tactics trainer stalls sometimes..?

I've been having problems with the tactics trainer for over a very long time!! I even cancelled my membership because of it. I came back to Chess.com for the mentoring.
Mozilla Firefox is my browser ..... I tried other browsers but none worked with tactics, aany better or worse. It's just something I have to live with. My f5 button is getting worn out from using it and it doesn't straighten the problem out anyway!
I'm starting to use GameKnot for tactics training and it works much better.

The problems persist! I have sent the following e-mail to bugs@chess.com
To: "bugs@chess.com" <bugs@chess.com>
Sent: Saturday, January 17, 2015 5:07 PM
Subject: Tactics Trainer does not work properly
Mods, help, support? I am a paying member and I am having some issues with the tactics trainer. I use Chrome browser and sometimes the tactics trainer get's "stuck." I will make a move and it will tell me "correct move" and then just stops. It doesn't follow through until either A) Problem Solved, or B) Incorrect move.
I'm 99.9% sure I have had this issue using Internet Explorer as well.
Sometimes it will say "problem solved", but then doesn't move on to the next puzzle I have to hit refresh or reload. It feels to me like the 'script' gets stuck or something.
I am not mad about it and I am not accusing Chess.com of being the problem. All I want to know is:
1) Is this a known issue or is it only me?
2) If it's a known issue, is there a resolution?
3) If no one else is having this issue, then how do I fix the problem on my end?
It happens enough that it has finally prompted me to write this message. Please advise. Note > I have no issues in "live chess" or anywhere else that I know of.
Thank you.