Playing LoL makes my internet stop working

Greetings everyone, so for 3 or 4 weeks now, most of the time when i'm playing league my internet connection just stops working for like 10 minutes or something. I googled a lot about this problem and Riot suggested uninstalling Pando Media Booster and disabling P2P transfer. Since PMD isn't a thing anymore i disabled P2P but it didn't resolve the issue. Already asked my ISP if it's on their side, but they said no, and since it only happens when i'm playing LoL the problem must be on Riot's side. I would be greatful, if any staff member could give me a suggestion what could be wrong. I am playing this game since beta and never had any problems at all.
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