New email - linking group email addresses is now broken

I use web-based Outlook.  Have always - when wanting to send a mail to an existing group that I have already created - simply clicked in the Bcc: box when creating a new mail.  A window has (and still does) open with the names of my groups in the LH pane.  It is asking me to select recipients, but clicking on any of the displayed group names does not result in the group members' details appearing in the RH pane.  However, clicking on the contacts icon and opening groups shows the contents of my group in full.  If I click on the envelope icon there, a new mail will open with that group shown in the To: field.  I can simply click and hold and drag that into the Bcc: field.   So, I know that what I used to do DID USED TO WORK, but it no longer does.  Any fix for this please?