"I checked settings and options ingame"
I did, it was set to Unlimited FPS, I tried dragging it down, and up and... No difference. Also Minecraft vsync is off.
And in Nvidia settings adaptive Vsync is off. Anything that limits the FPS is OFF on my computer as far as I know.
But first time this happened, I was ingame, something was lagging me, and I quit to main menu, and then it was the first time i started seeing 30 FPS, it would be very logical IF it was the adaptive Vsync, but its not :/
(I also tried installing Optifine, no difference)