Hi Andrij,
I did some testing today, and I noticed that the user avatars that appear in the pop-up notifications are different from the user avatars that appear elsewhere on the site.
It looks like BP Better Messages uses a JavaScript function to get the avatar directly, rather than calling for the avatar using the regular BuddyPress PHP function.
As a result, any plugins that modify the BuddyPress avatars are ignored by BP Better Messages.
I wonder if it’s possible to get the avatar URL using PHP, then pass that string into the showMessage function in bp-message.js?
That would keep things consistent with the rest of BuddyPress.
Let me know what you think. I’d also be glad to help with testing.