Using the EDIT function inside Acrobat DC Pro (version 2020.013.20074) destroys compliant TAGs.
The slightest "edit" inside the PDF (no matter if it's one punctation edit or changing the color of a headline) destroys the compliant TAGS, creating empty tags and leaving content without tags (which had perfect tags prior to the edit). We have done testing for this on cross-platforms with the same result (PC and Mac). We have tested before and after adding the required extra metadata. Same result. We have tested this with PDFs that originate from Word as well as those that come from InDesign. Same result. We believe that this is a software issue, a bug within Adobe's Acrobat DC Pro software.