For indexers it would check every 15 minutes, except when it start failing, which will incrementally block the indexer, up to 24 hours. If it failed in Sonarr consistently and was disabled for 24 hours, but it started working again during that period Sonarr wouldn’t automatically fix it until later.
I mean specifically for Sonarr connecting to things, old certificates used in SAB will trigger Sonarr to disable TLS 1.2, which would cause indexer issues, but not DNS issues like you’re seeing.
Try it in Internet Explorer, any proxies set in IE will be used by Sonarr and IE should show similar issues.
Have you tried different DNS servers? Especially if you’re using the ISP provided ones.
Have you tried without the VPN? If you’re not using public torrent trackers SSL should be enough.
The request was aborted: Could not create SSL/TLS secure channel.
This looks like TLS 1.2 has been disabled.
If you’re using SSL in Sonarr to connect to SAB or other local services with self-signed certificates try connecting insecurely.
I’m a bit hesitant to recommend it since it’s still beta (though very close to replacing v2), but you could try the v3 beta, which if something is causing Sonarr to drop TLS 1.2 it won’t happen in v3 because it’d instead drop the weakly secure connection. If you do decide to try the beta self signed certificates on things Sonarr is connecting to will fail out of the box as Sonarr enforces certificate validation in v3, you can disable it if necessary.