We never use to have this problem. We have some documents that need multiple signatures. Now the first person is able to sign, but the very next person who attempts to sign ends up deleting their own signature as well as the previous person's signature. This is happening to multiple people.
The process starts like this. A form on SharePoint is printed to PDF and sent to a person via email for a signature. The person downloads the PDF and then signs the PDF with their PIV certificate. The document is saved with the signature, and then sent to the next person who needs to sign. The second person in the process downloads the document and then tries to sign. When Acrobat saves the document the new signature and the first signature are deleted from the document. There are no signatures.
We can not find anything linking this behavior to any change(s) on the systems. We have tried multiple people on both Windows 8.1 and Windows 10 machines using Acrobat Pro DC.