I've checked the configuration and it turns out some shortcode in the content was causing the indexing to fail. I'm unable to tell which one, but on the Advanced Options I've disabled the Execute shortcodes? option to prevent the problem.
Then I tried again, and it went through nicely: https://i.imgur.com/vw9v5kC.png
It says 1 item is not indexed, but it's just a miscalculation in the script, as the ajax responses in the console were successful.Best,
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