Yes, I can, I think.
What worked for me is to get the name of the custom field from ACF. Then I placed the name of this field inside square brackets in the region I wanted it to display — like a shortcode. And just like that, the full HTML content from the WYSIWYG field showed up.
Yes. Same issue. If I set my custom field to WYSIWYG, go to create a post with the field, switch the WYSIWIG editor from Visual to text and paste my iframe code in, when I switch back to visual, I see the rendered iframe content. However when I go to the front end, the iframe content doesn’t display. OTHER text like <h3>A Related Product</h3> WILL display, but the iframe code is stripped out.