Instances of a model may stop progressing through milestones for a number of different reasons. Use this information as a starting point to work with your administrator to understand why your instances are not hitting the milestones that you think they should.
The most likely reason instances for a model to stop progressing is that the model has been deactivated.
The other likely reason that a model is not progressing is that milestones are improperly mapped to underlying implementation. For example if you are expecting a milestone representing “Order Shipped” to be passed frequently in your order processing application, but your orders seem to be “stuck” at the previous milestone, then it is possible that the Order Shipped milestone was associated with an incorrect action in an integration that does not really represent the order being shipped. Work with your Integration Architect to verify the mappings.
Another reason this can happen is if the integration is waiting for an event to occur before it continues. For example, an instance could be stalled at a Human Task (in the Processes feature) and will not continue until the assigned user takes the required action.