When troubleshooting, one of the first things to review is the Conductor 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 cannot distinguish between the data and the parameters if the ampersands within the data are not surrounded by spaces.
You can also replace ampersands with a character string Conga recognizes as a substitute for ampersands.
If that doesn't work, consider creating a hyperlink formula field for testing.