Not rendering output

Problem/Motivation

I have installed Footnotes as normal and configured a Text format.

I am trying to use the feature the edit a simple Text Paragraph (as in the Paragraphs module).

I can easily add a Footnote now to a text field...

When I look back into the CKEditor pane after doing so, I can see the result clearly visible...

However, once I save the Paragraph, nothing is rendered except for two non-breaking-spaces...

What have got wrong here?