You don't get this "randomly".
There's a specific reason why the AFCAD data sometimes can't be found, and it's due to 3rd party sceneries having external configuration utilities to switch between different AFCAD configurations. Depending on what they to do switch, the change can or can't be detected automatically by GSX, and the solution is alwyas to "Restart and rebuild the airport cache".
Running the FSDT Live Update will also clear the airport cache so, if you are outside the sim already, it might be better to do that ( or manually remove the %PROGRAMDATA%\Virtuali folder ), but if you are inside the sim, it's best to Restart and the Rebuild the aiport cache from the Couatl menu.