Yesterday, I updated a site from latest-release +19 to latest. All went well, except I myself started getting lots of notifications about group messages for a group I am not in. I looked at the group inbox and the button to change notification level is not displaying correctly. I tried safe mode and there was no change. I also rebuilt again, with no luck.
It looks like this:
On another site I manage, the button looks like the below and when I change notification level no error appears in the console. Though I did notice the icon sometimes disappears - I think that is a known separate issue.