I would say that there is something in a firewall on the server that is doing this. You need to narrow down what type of field and what the content is that is causing it. Then you can have a discussion with the hosting company to find a solution.
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Accordions are a great way to group related information while allowing users to interactively show and hide content. In this video, Damon Cook goes in-depth on how to create an accessible accordion block using ACF PRO’s Repeater field.https://t.co/RXT0g25akN