Intermittent DNS resolution issues for Vodafone Germany WiFi Calling

Hello,

I am experiencing intermittent DNS resolution issues with Vodafone Germany WiFi Calling (VoWiFi) when using Control D as my DNS resolver.

The affected hostname is:

epdg.epc.mnc002.mcc262.pub.3gppnetwork.org

When WiFi Calling is working, the hostname resolves successfully to Vodafone's ePDG IP addresses, for example:

epdg.epc.mnc002.mcc262.pub.3gppnetwork.org. 60 IN CNAME epdg.epc.drz1.vodafone-ip.de epdg.epc.mnc002.mcc262.pub.3gppnetwork.org. 60 IN A 139.7.117.168
epdg.epc.mnc002.mcc262.pub.3gppnetwork.org. 60 IN A 139.7.117.170

However, at other times Control D returns only:

epdg.epc.mnc002.mcc262.pub.3gppnetwork.org. 60 IN CNAME epdg.epc.drz1.vodafone-ip.de.

without any A records being returned in the answer.

During those periods, WiFi Calling stops working completely on all devices.

The resolution issue is reproducible across multiple devices (Android phones and different network clients). Google DNS (8.8.8.8) and Quad9 (9.9.9.9) consistently return working results and WiFi Calling functions normally. Only Control D shows intermittent behavior: sometimes WiFi Calling works, sometimes it does not, with no obvious pattern.