ping spikes in game after a duration of playing

this happens every game I play. for the first 20 minutes I'm safe but after a game goes over that it can take anywhere from 20-35 minutes for my ping to start spiking up. it'll go from its usual 60 to 400 for half a second then back down and repeat itself a few seconds later. and this lasts until the end of the game which usually comes soon after.