1) Bone Scaling is causing issues:
Figured out how to upload multiple animations within one model through the Sketchfab Plugin but realized bones with scaling will persist on animation clips that have no scaling differences in their keyframes. I held this problem on Blender early on but keyframing all transformations at the beginning and end of each of my Actions fixed it there, though not here. I tried baking my actions but made no difference. Feels like the scaling keyframes of bones are being ignored here for animation clips that hold the same scaling throughout the animation.
2) Drivers for shape keys aren't Working:
I have a low poly vampire character whose facial expressions I'd like to animate. Knew I couldn't animate the UV coordinates so as a work-around I duplicated the polygon faces that hold the eyes and mouth texture & created a new UV map & texture for them. Using shape-keys I can scale up these faces just above the surface of the default head to change the expression or scale down inside the head to hide them. This works here but it'll only allow me to create one shape-key animation that will be shown on all Actions/animation-clips instead of individual ones per action. I thought the solution was to create Drivers for the shape-keys & link them to custom bone properties which works on Blender but am likely exporting them wrong as Sketchfab doesn't recognize them when uploaded via the plugin.
This user managed to use drivers making me believe it's possible but their post doesn't help me understand how, other than perhaps needing to export to FBX which I have yet do so successfully.
Cube model to troubleshoot scaling and drivers
CubeExample.blend (157.4 KB)