In my case my main hub is notifying me of an update to 2.3.0.123, but when I click that link it shows there is NO update. I see that the update has been withdrawn. My question is: Will this sort itself out later or does someone need to do something?
My dev hub does not show a update waiting at all. Both hubs are at 121.
If the System Message keeps showing there is an update, and you don't want to see the message, there is an option to dismiss/skip the version. That way the System Message is cleared.