Can you tell me if you are playing from mobile or computer? In the case of mobile i would suggest to force quit and re-open. In case of computer, clear cache and cookies. Be aware that in the second case you might loose all your boosters. In case they are purchased boosters we can replace them. You can find more info here
Also, to be said, make sure you are beating level 884 with all points you need (and stars) to go to the next level.