I also noticed another weird behavior after upgrading, if I don't logout as Admin normally after some time it expires and takes you back to the login page. Now since 1.16.2, it seems that the Admin session will still expire, however the page does not change and take you back to login page, you can see all the Admin buttons at the top, and only once you click them does it take you back to the login page to login again.
Please provide reproduction steps. For example on this forum the Testing Ground category is not visible to guests. https://community.nodebb.org/category/4/testing-ground. So if you browse this forum as a guest it doesn't show up on /recent and it won't be visible in the category dropdown on that page either.
Your quick reply (and example) made it easier for us to identify it as a layer 8 problem. Our subcategories did not have the expected rights. Sorry for raising this as a bug!
Possibly related to the new verified-users, unverified-users groups. If your forum had the require email confirmation setting on and you upgraded then registered-users no longer have posting privileges. This is done by the upgrade scripts. But if you reverted without doing a database restore then registered-users won't have the privileges back.