It seems the Connections user meta for your user account has somehow been corrupted. But a couple things do not make sense. ON a clean WP install, there would be no Connections user meta to become corrupt. When you say “clean install” you also mean a clean db too, correct? Even still there are checks to ensure the when saving a message that it is an array. That said, looking at the code, those checks could be more robust so I made those changes which should make it impossible for these error to occur.
If you’d like me to apply the changes to your site in order to ensure that they work as expected I’ll need your login which can be posted here as a private reply.