Linkedin.com
Linkedin is proud to be IPv6 enables since 2016 ( IPv6 at LinkedIn Part I, IPv6 Inside LinkedIn Part II, IPv6 Inside LinkedIn Part III: The Elephant in the Room, LinkedIn Passes IPv6 Milestone) but still there is a Probelm. Linkedin used Microsoft CDN which Nameservers donot yet support IPv6.
www.linkedin.com. 300 IN CNAME www-linkedin-com.l-0005.l-msedge.net. www-linkedin-com.l-0005.l-msedge.net. 240 IN CNAME l-0005.l-msedge.net. l-0005.l-msedge.net. 240 IN AAAA 2620:1ec:21::14 l-msedge.net. 84113 IN NS ns1.l-msedge.net. l-msedge.net. 84113 IN NS ns2.l-msedge.net. Both anycast NS donot have a AAAA record.
Those NS are part of Azure Front Door
dig +short a-msedge.net NS dig +short au-msedge.net NS dig +short b-msedge.net NS dig +short c-msedge.net NS dig +short cn-msedge.net NS dig +short dc-msedge.net NS dig +short e-msedge.net NS dig +short exo-msedge.net NS dig +short f-msedge.net NS dig +short fb-t-msedge.net NS dig +short fbs1-t-msedge.net NS dig +short fbs2-a-msedge.net NS dig +short fbs2-e-msedge.net NS dig +short k-msedge.net NS dig +short l-msedge.net NS dig +short m1-msedge.net NS dig +short msedge.net NS dig +short o-msedge.net NS dig +short q-msedge.net NS dig +short q-t-msedge.net NS dig +short s-msedge.net NS dig +short segment2-s-msedge.net NS dig +short t-msedge.net NS
And non of those NS servers have AAAA record. So even if a subdomain is IPv6 enabled those sites donot work from #IPv6Only