Thank you for your help. It had something to do with Setting > Forum > “ReCaptcha for logged in users.” I had this checked and when unchecked the missing sidebar reappeared. This also relates to a missing submit button issue I had.
Thank you! I didn’t use the plugin you suggested, but you got me investigating with the browser’s Web Developers tools. I saw an error or something about “recaptcha.” So I started looking at the recaptcha settings: Settings > forums.
There’s a check box that says “recaptcha for logged in users.” I had this checked. I tried unchecking this setting, and my “submit” button (and hidden right sidebar from a different issue) reappeared.
Thank you again.
Sorry. Can you get a better idea from this screenshot? Thank you. 
One more bit of information. The right sidebar disappears when a user is logged in.
