BuddyPress.org

Hi guys,
I have mentioned this previously and was hoping a few of the past WP and plugin updates may have resolved this, however it still persists.
I am running a multivendor site with WC Vendors, Woocommerce, BuddyPress plus other plugins.

When a member goes to send a private message to a member/vendor from either the members profile ‘private message’ button or from the contact vendor link in a woocommerce product listing, the message fails to send (please see video link below).

However if i go to my own BP profile, messages, compose and send a message that way it does send.

Not sure what is happening here. It used to work fine prior to BP4.0

Video of issue;
https://www.dropbox.com/s/kkxl2b2bm5vicy4/BP%20Private%20message%20issue.mkv?dl=0

thanks
matt