I faced the same problem with updating my forums to 2.2.2. on propulsion theme as well, and I found a fix on bbpress support forum that really worked for me. So I thought it`s a good idea to share it here as well. While Kriesi coming up with the proper fix in the theme update.
So if you forum disappears after update try to comment out lines 657 and 658 in /wp-content/plugins/bbpress/includes/core/theme-compat.php
should be these two:
if ( ! in_the_loop() || ! is_main_query() )
All credit goes to John James Jacoby who suggested it on bbpress forum :)