Sorry, but I just had a laughing fit. The alien, he looks like he's actually one of those Terminators from the science fiction film Terminator. They could also liquefy (some kind of mercury stuff)
My assumption is and has always been that the Blender glTF Exporter module has an error or does not process or can not process all relevant information. The FBX file and the 3dsm file can be exported without any problems and do not cause any errors. The people are produced by me as if on an assembly line - it's a standard process.
My idea would be to contact the developer of the Blender glTF export module to work with him on a solution. I don't know the export module, and I can't say why it might be. Where can I download it, how do I install it?
Perhaps it is important to mention in this context that the MSFS glTF format has a special modification to the "normal" glTF format. This is expressly emphasized in the documentation of the SDK!
Another approach is to create an animation group that includes both the bones and the mesh. In 3dsm, animations are created using the MSFS SDK tool "Babylon Animation Groups". The tool is called "Babylon Animation Groups:
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3dsm Babylon MSFS glTF SDK Tool - Babylon Animation Groups
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It is important that the mesh and the bones are brought together in an animation group. Otherwise there are just those aliens and terminators as seen in the video from Kev