In Ghost 3.35.0 added support for 'data-members-name' in themes but if the theme uses only attribute 'data-members-email' (e.g. Casper) you cannot register (error in console 'null is not an object' inside members.js).
Any other info e.g. Why do you consider this to be a bug? What did you expect to happen instead?
The 'data-members-name' attribute should be optional, not mandatory.
Most helpful comment
Fixed in 3.35.1 https://github.com/TryGhost/Ghost/releases/tag/3.35.1