You have to upload the sprite style ZIP to TDSM before attempting to load a metadata JSON in that sprite style back into the program. The next update will add an error screen that catches it if it can’t match the JSON to an uploaded sprite style, but right now the program just crashes when that happens.
So every time you launch TDSM, you have to upload your modified Time Elements sprite style ZIP 
before you try to load from JSON 
.
Let me know if that makes sense and if it resolves your issue!
Edit: Just to clarify, you are supposed to use the JSON from the exported animation. That isn’t a mistake.