I’ve just tested it on my installation but failed to reproduce the issue. Could you please make sure that there’s no conflict on your site? Could you please try to reproduce the issue on one of the WordPress’ stock themes (like Twenty Sixteen) with other plugins deactivated? If it disappears, then you can activate the theme and plugins one by one to see which one causes the issue.
You can also try to check the console tab of the developer tools of your browser to see if there are error messages on the page.
Also, could you please tell me the version of your ACF?
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