Lag spikes

I have a gaming computer and nerd-level internet. I use an ethernet cable to connect and my ping is usually 40. Yet I still get horrible lag spikes that usually happen when i'm in a fight. I bet almost half of my deaths in the game are due to lagging out during fights. It seems to happen mostly during certain champions abilities and ults. Like Kalista ult, most of Rek'Sai's abilities, Ekko abilities, Tahm ult, etc. The spikes last from 2-5 seconds, which feels like forever in a fight.

Does anyone else have this happen or know how to fix it?