Windows 10 PC Automatically changed Firewall from Domain to Public?

Dear Admins,

I work as a system admin for a small company and this is my new job. I replaced and configured the network firewall at a customer and after all the PC in the network got the faster internet connection with a new public IP address.

Some Windows 10 PCs were running during the change. If I reboot them now (from remote), they ask if the network is public or private and default to public after a while. Results in the fact that I can’t reach them via RTP anymore.

I have so many other PCs in the network which are using the same Firewall, Router, Switch, DNS, DHCP etc.,

Why don’t they recognize that they are in the same domain network as before? I didn’t touch anything but the new firewall, so obviously I missed something in the configuration. But what?
Thanks for your thoughts!