lag with stable ping

Hey. I have been playing league since season 3 and just now I started having a very specific problem that makes it very hard to enjoy playing the game. I stopped playing in January this year and decided to pick the game up today and it just so happens that I have a stable 40ms ping like I always had, and 60FPS on the 60FPS cap mode with high settings (I have a good computer). However, every 4 seconds or so all my actions inside the game in a gap of roughly 0.5 to 1 second are not registered in the servers. This happened to me in the first game coming back to the game and then I went and tested the occurrence on a practice tool game by spamming right click at the other end of the map, and many of my right clicks were not actually being registered. I really want to have fun playing a few games every once in a while but this is just not doing it for me, I need a fix or else I don't think I will keep playing the game.

Info that might be important:

• I play multiple games weekly and I don't have this issue with any other game.
• I use Ethernet and never had problems with it in years.
• League was working fine last time I played it before today, which was in January.