I've been using Google Music Manager for a while (years?) on Ubuntu 16.04 and 18.04 and suddenly today it can't connect. It asks for my login and password, then my password again with a captcha, then an MFA code, then it says "Couldn't connect to Google Play - Check your internet connection and try again" (screenshot below). The "Retry" button has no noticeable effect. I can reach other sites and services on the Internet just fine. I don't have any outbound firewall filters configured.
I tried tips from here and here -- no luck.
Here's a screenshot of the error: