Crash when champ mastery appears

When I got a lvl 5 mastery for soraka, the symbol came down and it would just freeze right there and nothing would happen. This was also similar to when I got it for Aurelion but for some reason it cleared up randomly. But now I can log in but the moment I do the symbol comes down and everything freezes.

It has happened again for Nasus lvl 5 mastery. I don't know what causes it but this time it is just not clearing up.