RE: Guides now not appearing in Guides App, only in 'Sandbox'
Hi Paul,
Several things might explain this behavior and I would start by auditing your security setup.
How are you controlling access to the guides? For example, have you assigned the Author role to your users (see docs)? By default such authors have access to all guides in an instance. If they have a restricted role instead (described here), that would explain why your authors can only see some guides. Users with the restricted author role can only see guides they have created or been shared with them.
If that looks good, check your security group(s) membership. To Ken's point, IT security changes can propagate down.
If that looks good, as a long shot, make sure the guides haven't been deactivated. A deactivated guide won't appear in the PC app but it will appear under the Inactive Guides view on the portal. You can reactivate them if accidentally deactivated.
We did deploy an update this week but that should not have affected your existing instance. But let me know if you or an admin upgraded your CDS instance so I can pull in the right people to help investigate.