As described, your iPad appears to have difficulty reaching some server resources via your internet connection. The potential causes are many; possible causes include, but are not limited to:
- Your WiFi Router firewall is unexpectedly blocking access to some some internet resources (restart router)
- Security software installed on your iPad - e.g., Norton (remove if installed)
- Your iPad is a centrally managed device that belongs to an Enterprise or Educational establishment
- DNS issues (change DNS provider)
- VPN Connection (disable if active)
If you are able, try using a different WiFi network - or if available, a cellular hotspot connection (mobile phone or MiFi mobile-broadband router).
You might try using a reliable recursive DNS service. Here are some to try (IPv4 and IPv6 addresses are included below - configure all four servers for the chosen service):
Quad9
9.9.9.9
149.112.112.112
2620:fe::fe
2620:fe::9
OpenDNS
208.67.222.222
208.67.220.220
2620:0:ccc::2
2620:0:ccd::2
Cloudflare
1.1.1.1
1.0.0.1
2606:4700:4700::1111
2606:4700:4700::1001