Hi, I'm writing this here because its an issue I came across and solved. it might be useful for others
Unfortunately this fix does have the side effect of loosing all your settings/addonsettings etc, But hey atleast it works again!
(adding as many alternates/tags as i can think of so people googling might catch this fix.
Issue: Flyinside Not loading in headset, Game runs and loads as if fly inside wasn't even there. however Logfile states no issues.
Alternate issue1: Flyinside stuck on Loading inside headset.
Alternate issue2: FSX stuck on loading inside headset.
Cause: Something to do with the .CFG files getting corrupted. (Enabling fullscreen mode inside headset).
Fix:
Close all processes: Steam / oculus / fsx etc
Delete all .CFG files inside your FSX appdata folder. C:/Users/Yourname/Appdata/Roaming/Microsoft/FSX
Specifically:
Cameras.CFG
fsx.cfg
fsx_Flyinside.cfg
fsx_se.cfg
fsx_se_Flyinside.cfg
Restart processes
Restart flyinside/fsx
Re-accept all addons etc
Enjoy!
Hope this helps people who get a similar problem