No credit for destroying a tower

I've been experiencing this bug frequently in recent game particularly as twitch (although it might have something to do with me destroying more towers when in play adc than when i play amumu jungle, as these are my most played positions). what happens is when i destroy a tower, sometimes only the minions are showed to have destroyed the tower when the side notification for deaths and towers happens. sometimes the minions wind up getting last hit, but even then i still am showed to have assisted in killing the tower. this has also happened when i destroy a tower with allies and sometimes everyone gets credit for destroying the tower (including minions) but me. I don't know if this is a bug or something I'm doing wrong, but any input would help, as I am doing my placements for the preseason and i understand that objectives help towards your score.

~Thanks