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- Press F12 on the browser to load the developers mode
- Click on Console(clear it if required)
- Observe errors(red text) and if the description is similar to "Error : No serializer found for class org.onap.so.bpmn.core.RollbackData and no properties discovered to create BeanSerializer"
This issue 'could' be associated with any one of the objects being used in the BPMN flows to be ,when it's declared as a java object but attempted to be serialized into the object 'RollbackData' without marking/declaring declaring it as serializable.