Menus not loading in menu editor, appear to be in database

I am working on a localhost dev server. For some reason my menus disappeared from the menu editor and site, although the menu items still appear to be in the database. I also cannot create/save new menus in the menu editor. When I do so, the page simply reloads and is blank. Here is what I have tried:

* cleared browser cache
* deactivated ALL plugins
* switched to a few different themes (I had been using X theme, but switched to 2016, 2015, etc. to troubleshoot)
* manually re-installed WordPress, following directions exactly
* checked database, relevant individual tables (wp_posts, terms, terms meta, posts meta)
* with all other plugins de-activated on the new installation, tried installing Uber Menu to see if that menu editor would load my menus (it did not; it just says “Please assign menu to the Primary Menu theme location.”)
* tried re-installing themes

One clue is that in “Live Preview,” my existing menu does appear, in every theme. However, I still can’t create/save/edit menus in Live Preview.

So, I believe this is some kind of database issue. I can find all of my menu items listed in wp_posts with a query:
SELECT * FROM wp_posts WHERE post_type = ‘nav_menu_item’;
It returned 99 rows and appears to contain all of my menu items.

Also, in wp_options, I did this query:
select * from wp_options where option_name = “nav_menu_options”
And it returned one item with option_value = “nav_menu_options” and option_value = “a:1:{s:8:”auto_add”;a:0:{}}”

I saw in this post https://wordpress.stackexchange.com/questions/78316/wordpress-default-menu-in-database that there should be records in this wp_options table for EACH installed theme. So I sorted the table by option_name to find all of the records for theme_mod_
For my X child theme (the original theme I was using), option_value = a:3:{i:0;b:0;s:18:”nav_menu_locations”;a:2:{s:7:”primary”;i:8;s:6:”footer”;i:8;}s:18:”custom_css_post_id”;i:-1;}

The strange thing is, the options for each theme are different, though the menu editor, primary menu selection, and menu display is not working for ANY theme, including fresh installs of 2014 and 2016. I am at my wit’s end!

Is that perhaps the magic field? How can I get WordPress to allow me to create, save, edit, and display menus again? Thanks so much for any help you can provide.

Thank you,
Jen