Intermittent DNS issues

I am experiencing intermittent network issues. A lot hints to DNS, but there's also something else.

During such an episode, I can't ping an external site, e.g. a national news site like the BBC; then, it's 100% packet loss.Interestingly, I even can't ping the IP address of this external site during such an episode; I used the IP address of the site, that was reported by ping prior to the episode.

So, if DNS was to blame, how come that pinging an IP address also leads to 100% packet loss?

After such an episode, which usually lasts maybe tens of seconds. In between such episodes, everything works just fine.

I have configured a wired ethernet connection in Network Manager with a fixed IP address, and two fixed IP addresses for the DNS servers. My machine runs a current 22.04.4 Ubuntu.

I am seeing a lot of messages like the one below in my syslog:

systemd-resolved[997]: Using degraded feature set UDP instead of TCP for DNS serversystemd-resolved[997]: Using degraded feature set TCP instead of UDP for DNS server

I am not using any VPN.

From some reading into various Google hits, I got the impression that either NetworkManager or systemd handles the specification of the DNS server.

A lot of the results discuss VPN, which is not the case for my. The two specified DNS servers are on the same subnet as my computer.For what it's worth, the DNS servers are Windows Servers, and I don't have issues on my Windows machine.