Post

The export uses the NLA hack that Blenders FBX exporter supports. Slot Link places all actions & slots on the NLA, with a gap between what are supposed to be separate animations in FBX. This is how the export ready NLA looks^^ It's absolutely unmanageable doing this by hand.

Note, I can lead a horse to water, but I can't make it drink. The exported animations may still be incorrect, depending on what you animate and what's in your scene, due to Blenders borked data-model.