You can ignore that 
I fly in VR with a G2 and use other things like FSR and Motion reprojection. Normally I have a stable minimum 30fps in VR, making things look smooth with motion reprojection.
If it was a graphic issue I would have the same fps drop when starting at the same place of the leg, using the same conditions.
‘something’ is somehow triggered at specific leg starts hammering the CPU.
Just to test I lowered my resolution in vr with 50% but that didn’t affect the mainthread ms at all.
The first bush trip where I had this was the Breckenridge to Mariposa one, one of the first original bush flights… but that was 2 years ago so i don’t know which leg I had that. What I did then was deleting all the bush trip data, do it again and then at that same leg I didn’t have the fps issue. But that would mean that everytime I encounter this issue at a certain leg I would have to start the trip from scratch again. But again that also shows that it’s not a graphical or performance issue.
The most recent trip where I had this happen was leg 7 of the Perfect Flight Japan trip. Despite the 10-15fps I finished the leg. When starting leg 8 everything is ok, if I start leg 7 again i get the mainthread at 63ms issue.
I have seen those fps drop over long flights posts, maybe they are a bit related, but even when I do a fresh restart of my pc and immediately start that leg I have the fps drop.
Thanks for the feedback btw, appreciate it.