Thanks for this - the problem seems to be solved!
A couple of points to add:
- There was an additional folder called FSDT_Cargo_Wagon which, as it was not on your list of what to *ONLY* have, I deleted it.
- Following your last instruction of starting the sim immediately after deleting the Virtuali folder resulted in a Couatl crash in-sim. After closing the sim I then re-ran the update Check, restarted the sim and there seemed to be no further issues.
Will test further to be fully sure this is solved.