Computer Workout Thinks Forever

Having been a diamond member for over 3 years i decided its about time i used a bit of what i pay for and improve my chess game! I am currently working through the beginner study plans, which are awesome btw, however whenever the need arrises to use computer workout it freezes at random points within the exercise, it is almost every game but the point at which it occurs is totally random! It is most frustrating as it seems to happen most often as im about to complete the exercise (im sure its just me whos paranoid lol) causing me to start over.

Basically what happens is; i make a move and the screen displays "computer is thinking". I cant say for sure it will continue to show this forever as i usually get bored after ten minutes and reset the game myself.

It would be greatly appreciated if somebody could advise what the best course of action is here please and im struggling to progress in my studies without being able to complete the assigned tasks.

I mainly use my iPhone but have tried and experienced the same problem on my Microsoft surface tablet and iMac.

Thanks

Craig