[Steven Zahm]

RE: I am seeing a message “NOTICE: Connections database requires updating. START” (which is a link). When I click “START” after a few seconds, I get a message that the page does not exist (on a page that looks like the Connections search page). Any idea what is causing this?

Ok, are you being redirected to the frontend of the site, meaning you longer in the WordPress admin. If you are that would be the theme’s search results page.

Try temporarily deactivating every plugin, including Connections. Then activate Connections, switch the to Twenty Seventeen theme and then do the upgrade. Does that help?