BuddyPress.org

I see you already have. From a quick look at the plugin I think this is due to the way it’s been designed in that it uses a separate folder for the message attachments and the entry in the Media directory is effectively a dummy entry so it’s not picking up the file thumbnail etc.

Fork and redesign the plugin.

Yep this happens with free plugins. Sometimes authors take time out and sometimes that turns permanent. I’ve been going through the older, majorly broken ones and forking them in order to get them back online for folks. But there’s a limit to what I can do. Right now I’ve got about four thaT I’m working on. I can add this to the list of potential resurrections but tbh it’s got a low priority in that it’s basically working as designed. In other words the main function still works and there’s not an opportunity for a quick fix. This one I reckon would need a redesign and that’s potentially a lot of effort.

You could always do what I did – get stuck into this coding mallarky and start writing your own plugins.