Hi mcowan,
I tried this by disabling Bookmarks in my General groups per the documentation and I was unable to duplicate the behaviour you are seeing in your environment. Can you perhaps attach a screenshot or list of all the settings from that Groups > General > Security Permissions page? Or did you do this on a different area other than General? I also tried it on the Admin section but still couldn't reproduce the issue. In each test, I was able to see the forum categories and posts within it.
If you can provide more details on your configuration, specifically from the permissions page and where exactly you changed it, I think that might be helpful so that I can try to reproduce this issue. Also, if you re-enable bookmarks, did it fix the issue for you, or do the topics and posts stay as missing? Did you try different browsers just to verify that it wasn't a browsers corrupt cache or something browser-related?
I also checked for any known issues around that but did not see anything, so I can only suspect this is an environmental issue at the moment as I've never seen this behaviour before, but I'm currently unclear on what environmental areas would conflict with that behaviour of the bookmarks option. If you're able to provide more information, I can try to reproduce it in my lab. Also, if anything gets too specific in terms of hostnames and such that you're uncomfortable sharing, you can consider opening up a support case so the details are kept private and then we can give a non-customer-specific answer back in here once we've found the root cause and resolution.
Sincerely,
Dustin Dauncey
Sr Support Engineer, Global Customer Success
Email: Dustin.Dauncey@ca.com
Phone: +1 800 225 5224 ,48385
Phone if outside North America - https://tinyurl.com/CAContactSupport
CA API Management Community: https://tinyurl.com/CAAPIMCommunity