Whenever someone replies to one of my (witty, always genius) comments their comment stays “unread” in the notifications/inbix tab, with a red dot on the bell in the bottom left of the main UI.
I think they only get marked as read if someone else replies to them or if I go into lemmy in my browser to Mark As Read.
You have to reply to them, mark as read by long swiping from right to left, or clicking the envelope in top right.