I answered about PMDG, since you explicitly said it happened with the PMDG 777, so that's a specific case where Boarding start with some delay, if you have PMDG vehicles, and you never said you don't have them, so I only had to guess.
Of course, there's no problem whatsoever with any other airplanes (provided they are supported by GSX or you have a GSX profile either provided by the airplane developer or downloaded from someplace or made by yourself) and nobody ever reported Boarding not starting with MSFS 2024.
Other than running an update CHECK in the installer, to be sure you have the latest version, there's nothing I can say more without a more precise report, of an actual airplane used, an airport used, which airport profile is used, and possible a diagnostic log.