I am logged in and looking at the docs for Volumes Reference. When clicking on the details page for the Pain Causing, Physics, or Audio volumes, I get You do not have access to view this page within the site.
Here are the links to the 3 pages.
Pain Causing .unrealengine.com/en-US/Engine/Actors/Volumes/PainCausingVolumeDetails
Physics .unrealengine.com/en-US/Engine/Actors/Volumes/PhysicsVolumeDetails
Audio .unrealengine.com/en-US/Engine/Actors/Volumes/AudioVolumeDetails
On the weekends Epic sometimes performs maintenance to the documentation servers, which could be causing those pages to return an error.
I will check on this again later today, but if it’s still not working we made need to wait for Epic staff to look into it further tomorrow morning (US eastern standard time).
I’ve made those pages public. Seems like they should have been anyway. Keep in mind that they are just reference pages for the properties in those volumes and not detailed with examples of use. Hope you’re not terribly disappointed.
The Simplygon doc you linked to is for our custom license users only. If you have a custom license agreement with UE4, let me know and I can follow up to see that you have the correct entitlements.