For awhile I self-hosted adguard dns server. It supports iphone profiles thus forcing iOS DNS. I eventually disabled it due to timeout issues specific to iOS. Issue was something DNSSEC related.
While reproing the issue I noted the average recursor round trip time from my OVH server hosted in Oregon to the default upstream DNS - Quad9 - was around 70ms. When I changed it to Hurricane Electric the roundtrip dropped to a steady 20ms. Later I changed it again to Cloudflare and the roundtrip was a consistent 2 to 3ms.
While reproing the issue I noted the average recursor round trip time from my OVH server hosted in Oregon to the default upstream DNS - Quad9 - was around 70ms. When I changed it to Hurricane Electric the roundtrip dropped to a steady 20ms. Later I changed it again to Cloudflare and the roundtrip was a consistent 2 to 3ms.