This happens occasionally.
I have not narrowed down the issue, but have noticed that it can happen when I carry out multiple changes in the object/process without saving.
E.g. Re-spied an existing element with a new spying method without saving, or if I have not saved a process after updating multiple logic or removing the action that was in focus/stepped through at a time. But it doesn't happen every time I carry out those actions.
I think it happens, when an application somehow changes/looses connection, maybe during a page refresh.
The solution during the design phase is save process/object before testing it. Sometimes if you stepped through from process into an object, updated it and then saved the object, the process needs to pick up the changes. Use the refresh button to do this and ideally save the process also before testing.
On few occasions I have had this when simply running the process, on these occasions it might have happened due to connectivity or a backup. Good exception handling with few attempts might help if this happens.
