@MsRedNebula I'm sure you can make something of this.
Yes, the animations work normally when i reimport them, even into other tools.
What seems to happen with my issues is, the animation keysteps and orientation are somehow misinterpreted, ususally the first keystep is 30 degrees off angle, the bone orientation seems to be falsely interpreted as well, also the keyframes are truncated in steps and shortened in length.
Tried with several bone root approaches, even dummy roots, to no avail. I gave up eventually and am only making static assets for the time being
(the bug occured only since the dec. TMTK update, before that it worked like it was supposed to)
So far the only thing i can see in your FBX settings is the (and i'm not a Blender user)
the force start/end keying and NLA strips. you could test to turn one of those off
but that's just a hunch, no expertise to back that up.
Did you try using a different Blender iteration for the upload? 2.79 or 2.80?
I think the root of all this, and this IS the same bug that occurs with 3Ds Max,
i'm sure now, is they tried to fix something for Blender 2.79, as that'S most commonly used,
and Blender changed some of its mechanics regarding bones and animation.
Which Blender version do you use exactly?