Updates in Activity page is not working

Hello,
when I try write something in the activity page at http://paroledimusica.com/activity/ the update is not published. The issue occurs with or without Buddypress Activity+ installed. This is an old issue, that occurred for the first time few years ago, when I installed the plugin for the first time. Then I uninstalled it but it did't solve the problem. Now I installed the new version, but this didn't fix it as well.
Can you please check what it the problem?
Thanks.

Filippo