You have a list with a Due Date column that is used to calculate a Reminder Date. That Reminder Date is used as the basis of a "Pause until Date" workflow named "Send Reminder".
Some user creates an item and the workflow initiates a long-running "Send Reminder" task during which no other instances can of that workflow can be initiated. The user later revisits the item and changes the Due Date. The workflow is not triggered due to the previous long-running task. The pending reminder from the prior workflow is now out of date.
Is the "Pause Until Date" feature broken when it comes to potential user changes as described? I can't see how this would be useful since we cannot know whether the source date will be changed at a later time and there is no way for the workflow to react to this change without some sophisticated hack for what seems like a standard use case.