Comment 39 for bug 1754671

> These systems are using dnsmasq not systemd-resolver.
> This was done for historical reasons; I'm not sure of
> the specific bug which caused that choice.

NetworkManager in Ubuntu 16.04 and earlier defaulted to integrating with dnsmasq. But on 18.04 and later, this integration has been deliberately replaced with integration with systemd-resolved. If you are overriding this default integration to force the use of dnsmasq instead of systemd-resolved, that is likely not a supportable configuration.

In contrast, any bug in the systemd-resolved integration in 18.04 that would force you to work around it by switching to dnsmasq is almost certainly an SRUable bug. If you can find the information about why you switched to dnsmasq, please report this as a bug against systemd (with 'ubuntu-bug systemd') and provide a link to the bug here.