Hi !
I would try to deactivate BuddyPress from the Administration if you can still access to it. Otherwise using your FTP access I would remove the buddypress folder that should be into the /wp-content/plugins directory of your site. I would then go within the admin to switch to a “TwentySomething” WordPress theme, download a fresh version of BuddyPress, reactivate it. See what happens. If it’s fixing the issue, then ask for help to the author of your theme. Otherwise, eventually redo previous steps to remove/re-download BuddyPress. Before reactivating BuddyPress, deactivate all other plugins. See what happens. If it’s fixing the issue reactivate the other plugins one by one until the bug is back. Once it’s back ask for help to the author of the plugin. Otherwise, try to find the error_log file with your host to see the potential error message.
I also advise you to read the Basic Trouble Shooting part of this forum topic:
https://buddypress.org/support/topic/when-asking-for-support-2/ (especially if you use bp-custom.php or the wp-content/mu-plugins/ folder.
FYI 4.4.0 just like 4.0.0 requires at least WordPress 4.6, 5.0.0 requires at least WordPress 4.7
