I've noticed this a few times recently so I think it's something that we should look into. Several users have contacted us when seeing this error:

"This site is already connected to a different WordPress.com user, you need to disconnect that user before you can connect another."

But when checking the connection, the site was connected but is actually not currently connected at all. For example:

Debug: https://jetpack.com/support/debug/?url=http%3A%2F%2Fwww.colerainesurestart.org.uk%2F
Internal ref: 753945-hc

It was connected originally on 2014/11/25 but hadn't updated with us since 2017/12/13. The site was connected to the user that is contacting us.

Seems like something's not right with the broken connection and the error message that we're sending when they try to reconnect.

Delete and reinstall has fixed each site experiencing this problem.

Other examples:
1745309-hc (Site: breakmytoys.com )

585295-hc (Site: annabellesattic.net )

1745646-hc (seerssee.com)

753945-hc (www.e-makul.com)

moved from 1697-gh-jpop-issues