Acrobat Pro DC treats text box like an object

Hey all,

I'm running the latest version of Adobe Acrobat Pro DC on Mac High Sierra. It's been working great since I got it, but recently I've run into a problem. I have a PDF that I use as a template to add text boxes when editing. Normally this is no problem, but sometimes I'll use the add text tool to add my text and save the PDF. When I re-open the PDF, one of the text boxes is no longer editable. Indeed, DC doesn't even treat it as a text box. The other text boxes are fine, it's just one of them that is exhibiting this behavior. I can't edit, copy, paste, delete, or even select the text. However, if I use the edit object tool, I can select the text, but not edit it. If I resize the box, and then close the edit object tool, and then re-open the edit text tool, the text has been returned to a text box, and I can work with it normally.

Other than that workaround, I haven't found a proper solution to the problem. I have no idea why this is going on. It doesn't happen consistently, and none of the other text boxes I add or remove show this behavior. It seems as though DC is treating it as an image or object, rather than an editable text box somehow. Am I somehow accidentally changing the text when I use the add text tool?