At some point today, I got the "Application has updated, please reload the page" message, and the problems started after that.
As an aside, I have noticed a lot of open source communities moving to self-hosted
Discourse for their discussion forums (e.g., React, Meteor, Elasticsearch, Mozilla). It might be worth considering. Aside from the great feature set and user experience, we would own the data and wouldn't have to worry about Google Groups bugs or a possible future shutdown.
Anthony