I have the same error in the system log:
user.notice https-dns-proxy [2158]: Stopping https-dns-proxy 2023.12.26-r4 on_failed_health_check ✓
user.notice https-dns-proxy [2158]: Setting trigger (on_boot) ✓
I tried to add this command to SSH:
echo "(sleep 10 && /etc/init.d/https-dns-proxy restart)" >> /etc/rc.local
But I'm not sure its worked because I still see this error, If I understand correctly I need to write this command to some file.
I checked AdGuard,Quad9 and everything still the same, not working.
Also I ping these domain names "dns.nextdns.io"; "dns.adguard-dns.com" from the router SSH and their IP without HTTP-DNS-Proxy and got response back, so from my understand its mean my ISP not blocking them.