After some hours of good perfomance with ~40fps the FS suddely slows down. Maybe there was a backround programm running on the same Mainthread.
One of the 24 CPU-threads is fully loaded. I think this is the FS-MAINTHREAD.
In this special issue, the game speed recovers after a few minutes. And come up to 50fps again.
You can see a olot more activity on every Core especially the darker blue graphs. This should be the kernel times. But I have no idea what this means.