"There are no workflows templates available" error but actually workflow exist

I am using SharePoint 2013 on-premise farm. The workflow manager 1.0 is installed although we do not build any workflow on that.

One a site collection, when user try to create a workflow on "Pages" library, the error "There are no workflows templates available" occur. Checking ULS log there is nothing useful

Microsoft.SharePoint.SPException: There are no workflows templates available. Please contact helpdesk at Microsoft.SharePoint.WorkflowServices.ApplicationPages.AddWrkflPage.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

By using SharePoint Designer 2013 we can see the workflows "Publishing approval" exist. I clicked on "Publish" button on SharePoint Designer, the problem is fixed. However, after some hours later, user call and say the problem recoccur. I checked with Designer the workflow still exist and no change for "Last modified time".

My question is,

1. How can we check whether a workflow have been published?


2. How can we "unpublish" a workflow?


3. Any event can lead to "unpublish" of a workflow?

Many thanks. Any input is welcome.