Cannot access UI by name but can by IP address

Hello, experts!

I am having a weird problem that I cannot seem to resolve. A couple of days ago I changed internet providers. With the new modem/router I made sure to rename my WiFi networks to match their old names. Everything works fine with the iPhone app. But I cannot access any of my 2 Volumio players (RaspberryPI 4) from the PC. I can see them in the router list of connected devices - both of them are there by name. Everything works fine if I use their IP addresses. What am I missing?