I typically fly 1 or 2 hour flights and when I am not using REX WF I don’t get this problem. I have many other add-ons in use, including AIG at a high % traffic injection. When I use REX WF, maybe 15 - 30 minutes into the flight, the FPS drops to between 5 and 10. I stop the weather sync in WF, switch on the native real weather in the sim, and my FPS returns to where it should be. Is this a simconnect issue, perhaps? Does REX WF use that? I have just tried the new Beta WF that has just been released and it is still happening with the new version as well.