It may be a problem with ISP or DNS.
Here are some ways to try.
- Restart Modem/Router (Turn off and unplug for around a minute) - Their IP should change afterward unless they are using a static one.
- Change their DNS, either they do it on their device or on their router. They can try to use Google or Cloudflare DNS since they are faster and normally better in structure compared to the DNS provided by Internet Service Providers here in the Philippines. Here are some instructions you can follow https://developers.google.com/speed/public-dns/docs/using and https://www.windowscentral.com/how-configure-cloudflare-dns-1111-service-windows-10-and-router
- Use a VPN - since both DNS and IP are changed when you connect to a VPN.
