The process is being terminated for this reason. It is correct, they did add a new variable, which was not there when the process was started, but the question I have is why is this a reason for termination?
They added a new field to one of the user task's assigned forms and now when the process tries to assign that task it decides it is best to terminate the entire process and all future tasks, a new field will always require a new variable what's the big deal that it did not exist before?
I don't see any reason to terminate.