1. Go to https://bbpress.org/download/ and download current bbpress zip or tar file.
2. Unzip or untar it, which will give you a “bbpress” directory
3. Ftp to your site. Rename bb-config.php to something else in your root directory.
4. go to “wp-content/plugins/buddypress/bp-forums/
5. In that directory, upload the bbpress directory (not the contents of it but the actual bbpress directory including its contents)
6. Rename bb-config.php back to bb-config.php in your root directory for your wordpress site
7. Go to *yoursite*/wp-admin/admin.php?page=bb-forums-setup
8. Tell it to reinstall bbpress using the existing file (and make sure it is pointing to the right path to find bb-config.php)
This fixed my site and everything is working again.