Steps to reproduce it:
- Startup 6.2 or prior version of Liferay
- Create a template for web contents
- Shutdown the portal
- Upgrade to master (7.0)
- Go to Control Panel/Web Content/Templates
Result: the template created is not shown.
If you also associated that template to a web content prior to the upgrade and you try to edit that web content after upgrading the portal, you will notice that the template field is empty.
LPS-52545 added a new field for DDMTemplates resourceClassNameId, but it's not filled properly during the upgrade so the value for old templates is null. After that the template searches includes that field with the proper value so it doesn't find old templates since the values don't match.
It's neccesary to perform an upgrade which fills those fields properly.