suddenly unable to tag emails in a folder

Hi,

I am confused: I was going to tag all my unread emails in a Maildir++ folder, and I try ";" which usually gets me "tag-message" or something like that. However, I am getting "No tagged messages" on this folder (at the bottom).

Exiting mutt and then coming back to the folder does not appear to make a difference.

Likely some setting has changed, but what and how do I revert it back?

Many thanks and best wishes,
Ranjan