MathML not accepted as valid content for heading (h4) element

Ace 1.3.2, Ace by DAISY app

The error was Minor, Best Practice, empty-heading with the text

- Element does not have text that is visible to screen readers
- aria-label attribute does not exist or is empty
- aria-labelledby attribute does not exist, references elements that do not exist or references elements that are empty
- Element has no title attribute
- Ensures headings have discernible text
- Headings should not be empty

The content of the heading (with additional context) was

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It appears that the MathML is being read as no text or as inaccessible text. This may be related to issue 398.

Thank you for any assistance that can be provided.