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- You can NOT activate a process if there are more than 50 Active workflow rules on that object already. Note: you can keep creating workflows if there are more than 50 workflows, but you will get stopped if you try to deploy a workflow from Sandbox, or activate a process. (See https://help.salesforce.com/apex/HTViewSolution?id=000181391&language=en_US)
Issues
Lots of known issues https://success.salesforce.com/issues_index?tag=Process%20Builder
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