Sounds like you're blocking the servers which are supposed to push the notifications to you?! I think that's called Google Cloud Messaging.
You'd need to figure out which blocklist you enabled that does this. And either disable it, or add an entry to your allowlist.
Or do away with GCM and set up your own push provider like ntfy and additionally use apps from F-Droid that support this different push provider.
Edit: https://github.com/AdguardTeam/AdguardForAndroid/issues/3486 and there are several other bugreports. Also make sure you've disabled battery optimization for the Unbound(?) app.