[Linux/Flatpak] Desktop client fails to resolve web.fluxer.app unless AsyncDns is disabled

Update after further investigation I was able to reproduce the issue again after a cold boot, but further testing shows that this does not appear to be a Fluxer/Flatpak or Chromium AsyncDns issue. While Fluxer was showing the gray window and repeatedly failing with ERR_NAME_NOT_RESOLVED, DNS resolution on the host also failed: The local FRITZ!Box DNS resolver returned NXDOMAIN for both A and AAAA records. The FRITZ!Box is configured to use Mullvad's extended.dns.mullvad.netresolver (194.242.2.5 / 2a07:e340::5). Direct tests against multiple resolvers showed: I repeated the test against extended.dns.mullvad.net 10 times and all 10 attempts failed to resolve web.fluxer.app. The authoritative DNS servers for fluxer.app themselves return the correct A and AAAA records. Interestingly, Fluxer eventually recovered by itself without being restarted once DNS resolution began working again, presumably because its existing load retries eventually succeeded. So the earlier observation that disabling Chromium AsyncDns fixed the issue appears to have been coincidental. The current evidence points to the configured Mullvad Extended DNS resolver returning NXDOMAIN for web.fluxer.app. I'll report this to Mullvad as well.