FabricJS object functions dont work after loadFromJSON

I’m saving my canvas in JSON, and storing it in firestore.

jsonResponse.fabricInfos = this.canvas.toDatalessJSON([some properties]);

I already tried with toJSON too

The save works, and on load it loads everything right on the screen, but all the functions I try to use on the objects give an error.

Exemple:

object.set({opacity: 1});

I will always receive: set is not a function…