Try this. Select another aircraft (maybe a Cessna) and set all the avatar options to default. After it loads up, exit the sim without changing aircraft. Reboot your computer, launch msfs, and now try selecting the T6. I wonder if you are exiting with the T6 selected and something is not resetting? I really hope you get this fixed.
I managed to have an avatar pilot in place, by selecting another pilot and pressing Restart. See what I got: He looks smaller and his hand is showing through the fuselage…
There was a conflict between TSI Service Buddies pilot mod and the F/A-18 Super Warrior mod I think. It was odd though, default pilot selection would also not work and various bugs would appear depending which mod was installed first, so I have no clue if there could be more to it.
I have a few aircraft from the marketplace which are unlikely to be the problem, but I can’t see the pilot in the T6-G and it really breaks the immersion when viewing the aircraft from the outside.