This most often happens because the PDF-editing application you're using isn't happy for some reason. Try installing a free copy of Adobe Acrobat Reader DC and using it to fill out the PDFs.There's also a known problem with Preview for Macs that causes text rules in form-fillable PDFs to permanently break. The best solution is to download a fresh copy of the files (contact me if you need help), install Adobe Acrobat Reader DC, and only open and edit the files with Acrobat Reader DC going forward.