BuddyPress.org

@tkserver,

Is there any sort of predictability to this? Can you make it happen on demand? Or does it just happen once in a while at random? I mean, if you can figure out a way to reproduce it that would help. Do you have the ability to “clone” your site onto your desktop computer and fiddle with it there? Of maybe onto a cheap lightsail instance?

The problem with sending private messages to multiple recipients may be due to bugs in an older version of BuddyPress. Make sure you have the latest version installed. Also try disabling other plugins to check for conflicts.
Hope this helps!