I think there are numerous Emacs variables here, in addition to some
crashiness, that makes it very difficult to inspect what's actually
going on here.

I don't really believe that the HTML parser is returning a circular
structure, but I just can't get Emacs to print it out, even after
twiddling `print-circle' and `max-lisp-eval-depth'.  Help, somebody?

Included is the offending "HTML".   Put it in a buffer and say

(setq a (libxml-parse-html-region (point-min) (point-max)))

and try to get `a' to print in the scratch buffer.