I am getting the same problem lately.
I noticed it is more prominent around mountain regions with trees. Thought it might be connected to trees, but it isn’t. I reduced trees to low, but it changed nothing. But it’s abolutely more prominent in regions with lots of hills or mountains.
It is very annoying. I get constant 50 fps, but every few seconds there is this mini freeze. Sometimes it’s ok for maybe 30 seconds, but then it starts again, every 5 to 10 seconds.