Solution
The reason behind getting a broken wire is because JavaScript Object Notation (JSON) does not accept 2 or more objects with the same name (Unlike LabVIEW).Look for any data types with the same name. If there are any, you need to rename them. You can not have two identical named elements for a JSON file.
Below you can see a basic example of a cluster which will not work with
Flatten to JSON function as it has two indicators with the same name.
In the example below, you can see that changing the name of one indicator makes the cluster acceptable for the function.