that you are, in fact, logged in.

There is, I think, a bit of lingering damage from last month's cyber attack, that may include the log-in subsystem.

I kind of expect to get silently logged out about once a day.

If you are logged in, you will see in the right-hand side, a vertical menu bar with items like "Add a Story', "My files", and such.

If you are not logged in, then first, you will be really confused because you can see everything here, you just can't touch it (Edit, Comment, Kudu, etc.)

If logged out, you should see a log-in box, possibly filled out with your name and stars for password. If not pre-filled, fill in name and password, then click Login. (Long ago, I found checking "Remember Me" brought me "bad luck." Forgot what kind.)
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The other possibility, is that the BC server is using a cached/saved page ... and that page doesn't think you're logged in. Log in ... yeah, again. If no-go, log out, and log in . Again. If still no-go, problem is maybe at your end. First try, restart your browser, or use a different browser.

Last try, save everything and do a cold (complete power down) reboot of your machine.

Last, last try, message one of the Admins for help.
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See also the blog post "Comment s" by Alice-s.