I have a feeling it may be related to Step #6, when the bbPress repair tool ‘Repair BuddyPress Group Forum relationships’ works only the first time it is run, subsequent attempts will not actually update bp_groups_groupmeta.id with the correct forum ID.
If and ONLY if in your WP database tables `wp_bp_groups.slug` is an exact match with the associated post for the forum in `wp_posts.post_name` then the 2089.2.diff patch will work as long as this forum was one of the group forums originally imported.
Diving into phpMyAdmin and looking at these values and manually updating them I think will be the best solution.