Extremely poor game performance, for reasons unknown to me.

(Christ, I posted under gameplay. Mods, please move this thread to support or something.) I think it's my first post ever on the forums. I've been playing this game for a very very long time, and since like... 7 months-ish, the performance of this game went oddly downhill for me. The game has random fps drop spikes down to 8 fps, FREEZES (both of those happen randomly and only once in the game yet they last for solid five minutes, somewhere between the 7-12 minute mark) where I have 0 fps and it often ends with me being all-ined or dying under a turret from doing some poke, I get randomly disconnected as if I had a problem with my internet connection, so I tried both LTE internet, and fiber, the same result on both. The game "loses connection" frequently during those low fps moments for a few seconds or almost half a minute, but my buds on TS3 can hear me, and I can hear them, so it can't be the internet, right? In general, I have around 60 fps (capped) at 1080p, lowest settings. In teamfights it maybe gets down to 45-50, so I don't think it's my setup being at fault here. So far I've tried every troubleshooting method, and nothing had helped me. Did anyone ever have the same issue, and managed to find a fix?