There seems to be a performance issue that make the game unplayable for me.

Interestingly I have not suffer from those over last few weeks and only seeing them now in June. (2021)

Don't know if that is because my character progressed or it's due to end of Season patch. 

I tried all that is reasonably possible. Full screen / window, different in game options, resolutions, limit amount of cores, V-sync no v-sync what have you.

End result is that the game slow down to crawl, with massive micro-stutter. Usually that happens after 2-3 missions, or even in the same mission if I will leave it in Esc menu for few hours.

Issues I have noticed.

Memory leak.

Game starts, I load the mission, memory usage is at 2.4GB, I press ESC and leave it in menu for few hours, it will grow to, 5GB+ (while paused!) , another missing or two and it's at 10GB+.

Single core on CPU maxing out.

Game starts fine. All cores at sensible 20-70% usage. Performance is great.  I play a mission or two. After that single core on CPU run's at 100%, rest is at 20% or so.

In neither of these scenarios my GPU  maxes out (2080TI) and stays at about 40-50%  usage.

It's a fun game and I enjoyed it but will the issues above it's unplayable sadly. Hope Dev team will want to address these issue as it would be pity to not play the game due to technical issues. And players may leave due to that too.