HTML pretty printing has change from using
<html><span class="math"> to
<html><script type="math/tex">, so we need to fix
In the meantime, this can be "fixed" by adding
(setq sage-view-start-string "<html><script type=\"math/tex\">") (setq sage-view-final-string "</script></html>")
but then of course you can't run old versions of Sage.