When records are downloaded or created, the mobile device creates record titles according to the title structure that has been defined for the app. This is then stored in the record data.
When the record title for an app is changed and this change is synced to the mobile device, the existing records will not be updating with the new record title right away, while new or edited records going forward will display the new record title structure. The reason for this due to how the records are stored within the mobile app's database.
The easiest way to get the existing records to display the new record title structure is to reset the record cache on the mobile device and then sync the mobile app.
You can find the option to reset the record cache in the data management section on the settings page of the Fulcrum mobile apps.