Major fps drops

Hey I just played a ranked and all of a sudden my fps where around 30 in base and 14-20 in minionwaves or teamfights. Normaly I have 80fps with the highest grafic possible but even when I lowerd the grafics in game the fps wouldn't change. And yes I had other programms like spotify or my browser open but I leave them usually open so I don't tink that thats the problem eigther. Does anyone knows this problem and how to fix it?
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