Views:
Behavior:
When a workflow user is processing a task, they find that the ability to use Annotations/Stamps is grayed out. 

Solution: 
By product design, signature stamps prevent further editing or annotations from being placed on the document, with the exception of adding another signature stamp.
It is best practice to ensure that the signature stamp activity is performed towards the end of the workflow when writing back to the form is no longer necessary.

KBA applicable for both Cloud and On-premise Organizations.