We’ve asked Apple for comment on the issue, although watchOS 7.0.1 doesn’t appear to have addressed the glitches. Newer watches (including this author’s Series 5) don’t appear to be affected. It’s also unclear if the problems affect Series 3 watches bought directly from Apple with watchOS 7 already installed.
There’s a good chance this will be patched in an upcoming release. Even so, it’s not a great experience for owners of a device that’s still considered current.