From public chat icon, I'm assuming you mean your "All Chat" tab is gone? You've probably closed it - that's possible now.
If that is the case, it's easily turned on again. Click the "Community" icon in the ribbon, and then click the "All Chat" button. You may need to drag it left or right to get it back where you want to; you'll need to be in edit mode to do so.
If that's not what's happened to you, post a screenshot, as that'll make it easier to tell what's happening.
You'll've probably clicked the button, rather than closed the interface directly. That doesn't require you to have your interface unlocked. These things don't close themselves.
Can't speak much to those flickers; could be anything. Feel free to share more detail on those, or if it's a visual artifact, a screenshot maybe. Anachronia shouldn't cause any issues though, save that it did add several hundred MBs to the cache, so I'd've recommended sitting in the lobby and l;etting that download before trying to play. That's a good idea in general,following every update.