Serious performance issues ?

Am I the only one experiencing serious performance issues ?
Like old age POE 1 ?
I mean, I know my PC is not the most recent, it still boasts a glorious GTX 1080, ryzen 3700X and 16GB ram. It's been a very long time since i haven't had a real performance issue with a game. POE 1 runs like a champ, with decent settings.
This one is a whole other deal. Reduced resolution, set nearly everything to the minimum setting, and even though the graphs show a nice 90-100 fps average, with all parameters being quite steady, the game is laggy as hell !
Also, this is not constant obviously. It was fine for 1 minute after turning down the settings, and became unplayable again after that.
Can't say where the issue comes from, but needs solving !
Cheers