Do you have a memory leak in the game by any chance ? after a while performance gets so bad that it becomes unplayable. My 32 gigabyte ram should be enough but it gets up to 100% ram usage very fast so idk …
This is known but difficult to track! It’s helpful if you can report this when in game using the In Game Bug Reporting Tool (ESC) and make a note of how long you’ve been playing and what you’ve been doing!
No worries I am aware, since my husband is also a programmer and told me. I just wanted to make sure that this is an known issue. I try and do my best to put the In Game Bug Reporting Tool to good use 
Thank you very much for replying!
1 year since this problem appear. Still no fix