I got recently some html-only e-mails, coming from commercial senders
which could not be viewed with mutt. I had to kill html2text in order to
unfreeze mutt.
Replacing /usr/bin/html2text by a symlink to /usr/bin/html2markdown gave
an instant workaround, the same e-mails were displaied instantly in
text format. /usr/bin/html2markdown is provided by the package
python3-html2text.
I tried to simplify the HTML files in order to pinpoint the failure,
without success. If you want I can send some samples which could not be
converted to text with html2text. Their common feature is the abuse of
tables to insert elements into the page, and a very bad syntax