Long ago, when this would happen, simply bringing the messages app to active state on the phone would solve this. But now nothing does, until either closing the tab on the computer and reopening it, or re-pairing the phone with the web interface.
Yes, I check the box on the web to remember the phone.
Yes, I’ve cleared cache and cookies on the web.
Yes, I’ve signed out on the web and signed back in.
Bottom line is that, with no material change from me, messages.google.com went from working without error for a year or more, to failing multiple times a day.
Anyone else seeing this? Suggestions to fix?