Having the same issue: Not on GoDaddy hosting, fine on localhost, but redirected to 404 on live when using URL fields on the options page. I have also used this setup on other sites, but not had this problem.
I attempted your debugging steps; there was no array output, the redirect to 404 occurred. If this is a server-level problem I’m completely stumped.
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ACF PRO’s Flexible Content field allows you to create smaller pieces of UI and compose them into whole flexible patterns. In our latest article, we show how to use it to create swappable site sections and integrate it all in a theme.https://t.co/ZRocH8oJSp