In a process model activity chaining is added some tasks are executing some tasks are breaking what could be the reason?
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As all 3 prior commentors have noted in various correct ways, you need to provide quite a bit more detail here if you hope for a meaningful answer.
1) info about your setup; 2) what you expect the user to experience (and why); and 3) what's happening wrong in your opinion and why you believe it's wrong. Just for starters.