Hi,
does this happen on a live site or a local install ?
Do you have the same issue when you use a Twenty something theme ?
Do you use some message related plugin or custom function ?
Give details: php version, theme name.
The issue is somewhere inside the ajax.php from the theme. I’m using a custom theme (Not online) on a local version of wordpress. Tried using the functions.php from the legacy template but there is no live update so I skipped that. (Messages doesnt send at all)
Edit: I fixed the problem with combining ajax.php from the old buddypress template with the new functions.