I doubt a DNS filter would noticeably increase CPU usage. We’re not talking about deep packet inspection here.

Such bugs have already appeared in the past. It’s only logical that this happens from time to time, as the creators of bitwarden don’t test the compatobility with 3rd party servers.

What is important is that they’re not deliberately blocking vaultwarden.

I’ve run caddy and traefik. Personally, I prefer caddy, but both are likely completely fine for your use case.

Traefik has the advantage that it can be configured with docker compose files, while caddy needs its Caddyfile as a seperate configuration.