Yup it’s really weird, restarting the leg from magic mountain it’s fine… after about 5 mins of flying towards Albion the frames drop off. If I start a new flight from Albion it’s like I was in JFK 
The thread I was looking at is here, someone mentioned birds spawn when you’re 30 miles out. It makes for fun reading if you’re into AI seagulls!
https://forums.flightsimulator.com/t/seagull-model-causes-massive-fps-drop-when-loaded/309427/4
Forgot about the custom scenery with the trip will try deactivating and see if this does anything.
Can’t wait for the next one 