SheldonNesdale

Same issue for me (17 websites down). So I went to the plugin archive, downloaded an older version of the plugin, connected to each website via ftp, renamed the existing plugin by adding a dot onto the end, and uploaded the slightly older plugin. All my websites are now back up. (I just have to remember not to update them until this bug is fixed).

Yes, it is always good practice to use a child theme. If you make customisations to a core theme, they will disappear when the theme is updated in the future.

No, Twenty Eleven will not become Mobile Friendly in the future but you can install a Mobile Theme plugin such as WPTouch to serve your content to mobile devices.

Near the top of the page is “Screen Options”. Open this section and ensure that the Featured Image widget is displayed.

To help you for your search for a solution, that area is called the main menu. The class is .menu. You’ll need to learn a bit of css. You will also need to install a plugin like “Custom CSS” to enable you to insert css styles to override the defaults.

I am!

I think I’ve figured it out: Orphaned comments.

I had deleted several parent comments written by a troll, and all the comments written in reply were orphaned. Later, people wrote replies to the orphaned comments but they weren’t nested properly because there was no parent.

What a mess.

I deleted the last 200 comments and the nesting has come back.

You guys are awesome! I was scratching my head of this one. The solution that worked for me was replacing the wp-includes folder via ftp.