Blizzard has announced hat the upcoming 8.3.7 Build on the PTR will have no new changes or features for players to test.
A new build will be coming to the Public Test Realm (PTR) this week and will only contain non-player facing changes that are required for Shadowlands. We wanted to provide an advance notice that there won’t be any new features to be tested in this build.https://us.forums.blizzard.com/en/wow/t/upcoming-837-ptr-update/557081
It is possible that this build is putting systems in place for whatever big reveal was set to be shown on the canceled June 9th livestream. This livestream hasn’t yet been rescheduled, So this would be a great chance for Blizzard to implement some of the backend systems needed to support it ahead of time.