I found the problem! I’m just leaving this here for anyone else with the same issue who stumbles on this:

I managed to create a text field that WOULD let me tag it by creating a text box instead of a frame. When I exported, though, the error was still there.

Despite the deceptively worded error in the accessibility checker, the actual issue is that your form field is not in the articles panel. One nice thing is that this even exports correctly if you anchor the form field to other text in your document, which helps to maintain a sensible reading and tab order for complex forms like mine.

Hey David, thanks so much for the reply! What you suggested worked, but I don’t totally understand why it worked. I now understand that ^ means start of the paragraph, but what does GREP do if you don’t have that there? Is it starting from the end instead?