All smart functionality which a user can place inside a template for instance; Business Rules is in actual fact a chunk of XML that gets placed inside the templates XML.
Should the XML of a feature no longer exist inside the documents XML, the feature will no longer work.
Should a Business Rules no longer show up in the Business Rule right-side pane but the place holder still exist inside the template there are two ways that this Business Rule could have been broken;
1. The Business Rule has been copied from one template to the new template. When a copy of smart functionality is done, only the place holder and content inside is copied across, not the XML which makes up the Business Rule itself. Therefore, there is no manner in which DocGeneration can find or reference the rule inside the XML of the template and it cannot be referenced in the right-side pane. It will be an "empty" place holder inside the template.
Resolution: Do not copy Business Rules across templates again. Delete the Business Rule place holder which has no reference and create it from scratch in the template.
2. The Business Rule has been deleted from a template, immediately after, the undo feature in Word/PowerPoint (Ctrl + Z) was used to undo the action and bring the Business Rule back into the template. This will bring back the Business Rule place holder but not the XML and the exact same symptoms will be present.
Resolution: Do not use the undo feature when building smart functionality in the templates. Delete the Business Rule place holder which has been brought back into the template and create it from scratch in the template.