Adobe Signatures NOT Syncing

I have been using the same procedure for months.

Upload a pdf to Box, click send for adobe signature in the tool bar, place signature box on pdf and email to my supervisor for signature. 

This issue is on the occasions that I need to send more than 1 pdf for signature within a few minutes, my supervisor will sign them all, however Box will only Sync one pdf. 

This leads to me re-sending for signature later - which really frustrates my supervisor. 

What is a fix for this issue?

TIA!