When troubleshooting, one of the first things to review is the Conga Workflow formula field. The primary factors that affect this field’s behavior are:
Field accessibility (the field is restricted to certain profiles)
Whether it contains a value
The field contains or references fields containing ampersands that don't have spaces around them when intended as data
A field value of Ben&Jerry's will cause an error. However, a field value of Ben & Jerry's does not. Conga Workflow can't distinguish between the data and the parameters if the ampersands within the data aren’t surrounded by spaces.
The user who initiates the workflow process must have the "Send Outbound Messages" permission enabled, otherwise the email will not be sent.