All of the plugins have been updated, and I was able to locate the plugin with the conflict: Toolset Views. And before you tell me to contact them, please consider this: the issue is isolated to editing PAGES in Cornerstone, but is not present when editing single Layouts in Cornerstone, or archive Layouts in Cornerstone, or Global Blocks in Cornerstone, or Headers or Footers in Cornerstone. All of those work fine.
Here’s what else I’ve discovered: if I remove the header from a page, it then becomes editable. The Header has 2 dropdowns that contain Global Blocks with Views in them. No where else in the site are there issues. It’s something unique to editing Pages in Cornerstone that is conflicting here but I can’t quite figure it out. I’m just asking for some help troubleshooting.