alternate hosts are not being "recognized" when they enter a ZOOM I've created.

I create recurring ZOOM Meetings for Chairs of Committees. I assign the Chairs as alternate hosts in my meeting set up. Before yesterday, the alternate hosts would automatically be made the "host" of the meeting when they logged into it - I don't log into these meetings though I am the creator. 

Yesterday, two of our Chairs logged into their ZOOM meetings, but were not automatically designated as "host" and therefore not able to share screen or assign other co-hosts who could share their screen. Are we doing something wrong? This worked for the whole past academic year.