You need to pay attention to the expression and action you are using when dealing with tiles JSON. Objects have a common expression "AsJSON" that saves their entire state in a JSON string, and a common action "Set from JSON" to load their state from such a string. However, the tilemap have specific expression / action to save / load only its tile data, namely "TilesJSON" and "Load". You should be using "TileJSON" with "Load", or "AsJSON" with "Set from JSON", not a mix of both set.
Or maybe your problem is something else entirely, but we lack information to really help you.