BuddyPress.org

Yes there is, it involes a minor amount of code wrangling. First of all you need to install a child-theme. You can get plugins for that if you’ve not already got one. This will create a directory on your server called wp-content/themes/your-child-theme.

In that directory create a buddypress/groups directory.

The next step is to work out which BP Theme you are using. You can find that by looking in Settings>>BuddyPress>>Options.

Once you know that, you will be able to find a file called `wp-content/plugins/buddypress/bp-templates/your-bp-theme/buddypress/groups/groups-loop.php.

Take a copy of this file and find this part:
<?php if ( bp_has_groups( bp_ajax_querystring( 'groups' ) ) ) : ?>
Change that to:
<?php if ( bp_has_groups( bp_ajax_querystring( 'groups' ) . '&order=ASC&orderby=name' ) ) : ?>

Next you put this file in the themes/child-theme/buddypress/groups directory you created earlier.

The next step is to take a look at the error log, the easy way is to install an error log viewer such as BWS Error Log Viewer. Once you have that installed try registering then look in the log for entries at the same time as the registration attempt. That should reveal any PHP errors. Which BP Theme are you using? Look in Settings>>BuddyPress>>Options, the theme setting is in there.

What you could do is check if there is a thread_id for the new message, if it’s not set it’s a new message and you can remove the recipients so that sending fails.

function venutius_check_recipients( $message_info ) {
	$recipients = $message_info->recipients;

	$u = 0;

	foreach ( $recipients as $key => $recipient ) {

		// if site admin, skip check
		if( $GLOBALS['bp']->loggedin_user->is_site_admin == 1 ) {
			continue;
		}

		// make sure sender is not trying to send to themselves
		
			if ( $recipient->user_id == bp_loggedin_user_id() ) {
				unset( $message_info->recipients[$key] );
				continue;
			}

		/*
		 * Check if the the message has a thread_id, if not it's new and not allowed.
		 *
		 * If we get a match, remove person from recipient list. If there are no
		 * recipients, BP_Messages_Message:send() will bail out of sending.
		 *
		*/
		if ( ! isset( $message_info-thread_id ) ) {
			unset( $message_info->recipients[$key] );
			$u++;
		}
	}

	/*
	 * If there are multiple recipients and if one of the recipients is not a
	 * allowed, remove everyone from the recipient's list.
	 *
	 */
	if ( count( $recipients ) > 1 && $u > 0 ) {
		unset( $message_info->recipients );
	}
}

add_action( 'messages_message_before_save', 'venutius_check_recipients' );

You coud put this in your child themes functions.php or if you want it to apply to any theme, add it to your bp-custom.php in the plugins directory.

You can put it in the functions.php file of a child theme.

Yep you need to ask the theme author if they can fix it.

afaik, by default BP private messages do not have a Title field.
They do have a Subject field.

Are you using another plugin or a special theme that uses a Title field ?

On a standard BP install, if you forget to fill in the Subject field, the message will not be sent and an error will be displayed.

Probably a conflict with other javascript on your site.
Did you check your browser’s console for javascript errors?
Did you try switching momentarily to a WP theme like 2017 and retesting to see if there is a conflict in your theme?
Did you try deactivating other plugins and retesting?

This is probably down to your theme or a plugin overloading the registration page.

Yes. Or bp-custom.php