It seems like there are several issues in connection with FPS drops. Please post in the corresponding thread in order to avoid confusion.
1.) The one OP is referring to. Around 30% less frames compared to SU8. I myself have the same issue. Instead of 40, I am now at 28-30 with lots of stutters. (This thread)
2.) FPS loss after longer flights (this was a problem before SU9 already)
3.) Stuttering/low FPS on the ground due to constant Logbook access (also before SU9 I think)