BuddyPress.org

Read this:
https://buddypress.org/community/groups/how-to-and-troubleshooting/forum/topic/how-to-definitively-display-buddypress-avatars-in-bbpress/

Make sure you have enabled deep integration in your external bbPress install:
https://bbpress.org/documentation/integration-with-wordpress/#func
or:

Deep integration of bbPress with WordPress