Steps to reproduce
Create 3 spaces: A, B & C.
Create a Viewport collection with A being the root space and B&C being members.
Activate Scroll Versions in space B. Do not make any versions available in Viewport on the Versions screen.
Make all of the spaces available for anonymous users.
Try to access any of the viewports in an anonymous tab.
Viewports A&C are accessible to anonymous users, viewport B is not.
All of the viewports fail to display. See error in attachment.