This problem ONLY concerns IE11 and on a SharePoint site using the bootstrap theme. When you create a Team Site and add a Task list, the ribbon is disabled and either the Tasks nor the Timeline is visible. If you open the same site in IE10 or Chrome, it is visible and working.
The site is added into the Compatibility View Settings and if I apply the Default Theme then it all works so it must be something in the bootstrap CSS files or JS that is blocking.
