I have WPForo and BuddyPress (but issue was same with bbpress) And if somebody reply on topic when i have subcribion, i have in notification menu blank title. Only Date and time send and action menu. In my Database in wp_bp_notitications is
id 13677
user_id 3
item_id 394
secondary_item_id 49
component_name community
component_action wpforo_new_reply
date_notified 2018-09-24 13:48:17
is_new 1