I can see "ORDER BY t_cascading DESC,t_pinned DESC,t_cache_last_time DESC" goes into the cns_render_forumview function but not through to cns_get_forum_view, even though the $sql_sup & $sql_sup_order_by parameters are passed through without changes.

This suggests sources/cns_forumview.php is altered.
The stack trace shows it as non-overridden, but possibly that's due to the way you've overridden it (per-function override?).

Here's the commit where the changes were made so you can see what may need changing in overrides:
https://github.com/ocproducts/composr/commit/cc12ba513bba98470c46c9ab9df8cbc37306d74d#diff-b5d6972d58c1fcf3a46a522925df290c

Unfortunately sometimes we do have to change compatibility within internal files in patch releases, overrides always come with a risk.

I didn't have those changes to my cns_forumview file - this was causing the issue.

I made the changes in your commit and now it's working. Thanks!