WiFi calling not working in a location where it previously worked

I have been using WiFi calling both at home and at work, due to weak cellular signal in both locations.  It continues to work fine at home, but within the last week it stopped working in my office at work.

I have a very good WiFi connection at work, and internet performance is good there (56 Mbps download; 12 Mbps upload).

We are checking with our office ISP to verify they are not blocking VoIP traffic, but we are not aware of any configuration changes.  We did not make any configuration changes to the office LAN.

Did AT&T recently add any restrictions to WiFi calling?  We are located in northern Illinois, in the town of Willowbrook.