I was having some issues when I use desktop alert since some time. I was not able to reply or post as well. Now I am using a different browser and disabled desktop notification. It is working fine. Please check.
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!