BuddyPress.org

BuddyPress activity replies only work when javascript is enabled. This is a known issue:
https://buddypress.trac.wordpress.org/ticket/3705

The problem is your theme (and/or plugins) is conflicting with BuddyPress’ javascript. If you check your browser’s debug console, you should see some javascript errors.

Try to nail down where the issue originally came from. It should be a plugin or your theme’s JS that is the culprit.