Normal game visually slowed down every minute or so.

I've downloaded the 7.5 patch and played a ranked game. All good, no issues. However, I've joined a normal game, and every minute or two, the game would visually slow down, and eg. movement would be slowed and then the champion just appears at the destination upon true arrival. Everything I see is in slow motion, except for the actual landing of spells and movement. I have to restart the game every time it happens, so I get behind and cannot play properly.