"Check for Updates…" doesn’t find new beta updates

[gorem]

I am on the beta channel: Version 5.1a2 (3004). 5.1b1 is out, and in Preferences, I have the “Test builds” radio button selected next to “Download:”.

But clicking “Check for Updates” just gives me the pop-up saying, “ You’re up-to-date!” and “NetNewsWire 5.1a2 is currently the newest version available.”

This is on macOS Catalina 10.15.6 (19G2021).