Honestly FBX problems exist because of AutoDesk and this is also one of the very reasons why glTF exists, collada didn't do the job well enough and everyone was getting sick of FBX issues.
AutoDesk does put out an SDK for motionbuilders fbx but they also keep changing specs rather arbitrarily every year so it's a huge pain to maintain support for, if you even can since the license itself is a pain too.
There's a reason why blender community just reverse engineered and developed their own importer and exporter from scratch. It's cause blender is GPL licensed and AD decided to outright make their license completely incompatible. Explicitly.