I have my animation settings set to 'not repeat', and there's a glitch as the final frame plays.
It looks like the static pose image is being flashed right as the time line runs out.
This FBX was animated and exported at 30 fps.
I tried changing that to 24 fps and re uploading, but nothing changed.
If I switch the SketchFab viewer from seconds to frames, there is no glitch.
I have no clue why that helps.