Drop down in editor says "undefined"

I’ve been using the CF7 form on this site for a few months. Now, when I edit an existing form or add a new one, the drop down to give the different parameters isn’t there. Just a broken image link with “undefined.”

If I bring up developer tools in Chrome, it shows some errors for missing images in the wp-admin\undefined\images folder. But there is no “undefined” image folder.

Anyone else seeing this? I’ve removed CF7 completely and re-installed. Also deactivated and reactivated all plugins. This is my own custom theme. Can’t figure this out.

Any ideas appreciated!

https://www.ads-software.com/plugins/contact-form-7/