Adobe Acrobat DC Pro Export to Excel

You may want to file a bug report: http://www.adobe.com/products/wishform.html

In general, exporting a PDF file to antoher format is one of the most complex tasks you can do with a PDF file, and the results depend highly on how the file was generated. If you started out with an Excel document, and used Adobe's tools to convert to PDF, and then try to export from that PDF again, you will usually see the best results. For other documents, Acrobat needs to analyze the structure of the data, and that's where things can go seriously wrong. Just because it's obvious to human eyes what should belong together, and where rows and columns are, that does not mean that a computer program will make the same decisioins as we do. It is possible that the change in behavior between the 2015 and 2021 version is due to an attempt to make other cases be handled better and your case just is an outlier. 

What I usually do when I end up with a bad result is to export the PDF page as a high resolution image (e.g. a 600dpi TIFF image), and then I import that image back into Acrobat and run OCR, and then I try to export again to MS Word or Excel, and oftentimes I get better results. There is also a dedicated free application that allows for a better data extraction than what Acrobat does: https://tabula.technology (but it's also a bit harder to use than Acrobat's one click approach)