There is a known problem if the Alfresco connected app definition in Salesforce has been configured with the wrong lifecycle class. If the lifecycle class is not set to AlfrescoCanvasLifeCycleHandler, all record folders in Salesforce are created with IDs that are 15 or 18 characters in length.
Edit the Alfresco connected app definition, as specified in Step 3: Configure app in Salesforce and ensure that the lifecycle class is set to AlfrescoCanvasLifeCycleHandler.