Unable to add multiple signatures to document - Adobe DC and XI

Hi, I have a pdf form with signature fields which gets signed off at various stages of a project. This has worked fine for a couple of years until last week....

Now, when the first signature is applied it works fine, however when they try to apply a subsequent signature they have to browse the network to find their signature - once they have done this and signed the document they have to repeat this process every time they try to sign.