Errors in Classic Editor after update to WordPress 5.5

After the automatic update to WordPress 5.5, I suddenly could not access some features of the Classic Editor. I am using Woocommerce with the Booklovers theme.

When editing products, posts, and pages I was unable to access the current screen for the Media Library to make edits to the featured image. Instead the program forced me to an older version of the same screen, stripped of easy-access features. I also could no longer toggle the different windows within the Classic Editor. I am not using the Classic Editor plugin; instead I simply disabled Gutenberg throughout my site.

Testing revealed several JSON errors, including an unexpected end of data error (it looks like two brackets are missing in the JSON but I’ve no idea where exactly). The Enable jQuery Migrate Helper plugin identified Essential Grid as the affected plugin, and when I deactivated it the problem was resolved.

This is a heads up to your team and to other users that the JSON for this plugin is no longer compatible with the Classic Editor (not the plugin version, but the version that is accessible when one disables Gutenberg either through the Dashboard Admin settings or through theme settings. Please let us know when there is a fix available, as Essential Grid is usually very helpful when working with my site.

My particular issue is resolved.