Communication Site - Highlighted Content > Pages > Managed Property Empty

Thanks for this thread, lots of good helpful information here.  Just to report my experience.  We have a Communications Site where News pages are published in the Site Pages library as a central repository for other site collections to pull from.  I set up the Managed Property + Highlighted Content web part machinery outlined here and got it all working as intended.  No small task.  However today one of our Team Site owners found her HC webpart will not populate the Managed property name dropdown even using exact same settings as the other 3 site collections where things are working fine (including another Team Site).  Why would this fail for one site when several others are working?