Digital Signatures Unresponsive in Reader

Scenario: Adobe Acrobat Reader becomes unresponsive when using a digital signature. 

Background- 

Version; Adobe Acrobat Reader 21.001.20135

OS: Server 2016

Delivered via: Citrix XenApp published icons

The problem started about 1.25 years ago, the program will allow you to 1- draw the position for the signature on the doc. 2- Select the certificate (ours is being pulled from our CA server) then 3- process to the preview screen.  however nothing happens after that when the user clicks 'Sign' generally speaking they would be prompted to save the document and a file explorer window opens. However if the user is affected then when they click sign nothing happens. There are no pop-ups or messages displayed. The program though is otherwise useable, the user can saves as or open a new file etc, just the signature does not apply.