Rich Text Editor toggle is disabled (silently) on specific entity bundle: cannot re-enable

G'Day all,

On a custom content type we used the default body field to store text. I imported 1000 nodes using Feeds Importer, and the format for the body field was set to Full HTML.

After import, I wanted to edit text in this field and found that I had no CKEditor toolbar (logged in as User 1). In fact there was not even the toggle for show/hide Rich Text Editor. Setting the input format to various Full, Filtered, Plain text had no effect. The form element was not refreshed; no Rich Text Editor toggle was displayed; nothing except the plain input form.

CKEditor is working normally across the site (in blocks editor, Panel-pane editor, and other content types) so we can eliminate issues with CKEditor itself (I think).

I created a new entity type which also uses the default body field, and CKEditor appears fine. So we can say that this Drupal install has a functioning CKEditor and the body field is capable of toggling between plain text and rich text input. In selection of rich text input, the body field is enhanced with the CKEditor toolbar (on the new test entity) but NOT on the problem entity.

Next, I created a new field (long text w/summary; widget = text area). When this test field is placed in the test content type we get a normal situation. When it is placed in the problem content type, we again lose the rich text toggle and no CKEditor is displayed.

So this test shows that it is not a problem with a specific field.

All that I'm left with is thinking that something in the entity definition has been corrupted and now *no fields* are allowed to have rich text input.

But how can this be? What can I test further?

Attached is a text file of the blob for the two entity bundles (test and problem) with the field config instances. Strangely, the instance for the problem entity is about twice as long as the test entity.
But I don't know what to make of this information. I was just hoping it might be useful in some way.

Any thoughts or clues?

Thanks indeed,
JB