Thanks for the help everyone!
There might be issues with the animation or mesh; however, I don’t think that is the whole picture because animation blending does work fine when I blend the animations in Blender.
I experimiented a bit.
I found that deleting the Z quaternion rotation key frames for
mixamorig:RightShoulder in Blender and then exporting it as .bablyon produced good animation blending. https://playground.babylonjs.com/#14XU5B#3
It seems odd to me that deleting rotation data fixed not only the bad rotation but also the bad scale values in the animation blending. Is it just me, or does that sound like a bug?
I also was able to get around the glitch by adjusting the Z quaterion rotation values. If I adjusted all of the values to be below 0 or far above 0, then there were no issues with animation blending.
Original values (broken)
Below 0.0 (working)
Above 0.0 (working)
The problem could be with the Blender to Bablyon exporter.
About the “
animations.from + 1”, I found that if I didn’t do that then the animation didn’t loop properly. That could also be a problem with the exporter, perhaps.