Same issue in beta 8. Only occurred when beta 8 installed, I am using an iPhone6+. Bug filed under #28059466.
Please reference the number above when you file your bugs so we can make sure the entire team can see the issue is pervasive and not hardware related.
Also some things I suggest:
Use a second device to make videos of the issue.
Upload those videos (zipped) to the bugreport
Drag all logs from the Phone (Using the Window > Devices menu of Xcode beta) onto the desktop
Put all the logs into a folder, compress that folder and upload to the reported bug
Reference the bug number and share your own bug numbers so I can add to my incident.