Open a document and receive 'Could not resolve field for name <FIELD_NAME HERE>

The field that cannot be resolved corresponds to a modified template that is not yet up-to-date as far as the content goes.

STEPS
1/ create a document type

• in this case I work with a new namespace 'ns' where I create a new document type in which I insert a simple String
• update all content

2/ create a new document based on this type

• publish it
• close its tab

3/ modify the initial document type

• in this case I added a simple date below the String
• click Done
  Note: don't update all content yet!

4/ open again the document you created

• nowhere do you see the additional field

In the Tomcat Console I see:

ERROR [org.hippoecm.frontend.editor.plugins.field.FieldPluginHelper.<init>():75] Could not resolve field for name date