Hi folks,
I wanted to post here as well for visibility and discussion purposes.
Per today's blog post the registration for 2.7.x releases of Sourcetree for Mac will stop being available shortly. In that you'll find a workaround that enables you to skip that particular registration flow so you always have a way to install those versions.
All other versions, on both Mac and Windows, are unaffected.
Brian Ganninger
Principal Developer, Sourcetree