Certain browsers (i.e. Safari 9.x on desktop; Safari on iOS 9.3.5, 10.1.1, 10.2.1, 10.3.2, and 10.3.3; possibly Firefox 66 on Android, but that report might just have been due to the checkbox being hard to see in that browser) don't allow sites to use local storage in private or incognito mode.
That means that when a guest checks the box and presses the accept button on the Terms of Service prompt, the prompt just sits there and stares at them and they never get to see the actual site.
Using one of the aforementioned browsers in private mode, visit a page and make sure the TOS prompt goes away and stays away after you accept.
Using a browser not mentioned above, also in private mode, do the same.
Bonus: Use your developer tools to determine whether we’re setting a cookie or an item in local storage, and let us know your browser and operating system or device.