Purifier duplicates anchor tags - trix-editor generated html

Hello,

I am just implementing htmlpurifier to sanitize the html generated by the basecamp:trix-editor.
After purifying, it duplicates the anchor tag in 5 various places (apparently inside every other element).

Here is the code I used:
https://gist.github.com/AntonioPrimera/ab8646567bac2b81c09298a83bc50532

Here is the original html:
https://gist.github.com/AntonioPrimera/4e6c421aecc94589474d6b2602282505

And here is the purified html:
https://gist.github.com/AntonioPrimera/ca5f6c6e1c93231a78f588fb82f4c57d

This seems like a bug, rather than a wrong configuration - I think no configuration should allow tags to be duplicated.
Any help / hint is highly appreciated.

PS: I have also tried disabling Tidy, via $config->set('HTML.TidyLevel', 'none'), but the results are the same (with or without the Tidy functionality).
PS2: When I remove the figure and the figcaption elements from the config, the anchor tag is not multiplied. Is it maybe because of the way the anchor tag is defined: strict - accepting just text / img tags inside?

Start by reproducing the purification shown in the linked code gist, comparing the original and purified HTML. Focus on the interaction between anchor elements and the configured figure and figcaption elements, and verify that removing those elements prevents duplication; done means the purifier no longer duplicates anchors while preserving the intended sanitization behavior.