That was it! For some reason the attachments panel previously showed up for my custom post type even though I had not specified it to do so in the custom instance. When I added it to the array in $args it showed up right away. I should’ve been paying more attention to the $args variable. Thanks so much!
I created a custom post type called “resources” using the Custom Post Type UI plugin. After upgrading, when I try to add or edit a resource the My Attachments panel does not show up in the admin. But the panel is still there for both posts and pages. Also the attachments I had attached to my resources before upgrading are no longer showing up on the public site.
