Radio buttons not working on setup

When creating an iframe popup, on the main page, under when to show popup, etc, the radio buttons can be selected but, once selected, they cannot be unselected.

Show popup when page loads is pre-selected, and cannot be unselected. Also, any other radio buttons on that setup page, once selected, cannot be unselected.

I’ve tried both Safari and Chrome with same issue. Running WordPress 5.6