Lovelace built-in editor suddenly stopped allowing saving changes

I have been using 2022.3 for almost a month. All of a sudden, the Lovelace editor no longer permits either saving changes or cancelling. I was editing yesterday just fine, but now the Save and Cancel buttons have no effect, and I have to reload the page (with changes unsaved).

I have tried clearing my browser cache, and using a different browser, and even a different computer, to no avail. I can edit and save in the Android app on my phone, or in the raw configuration editor.

Any ideas what is causing this, and how it can be fixed?