I'm going to assume that you have used the following condition in your Processing Rule:
Query String Parameter utm_medium=D2C Exists
If you're using that, then that's wrong. It makes AA look for a query parameter "utm_medium=D2C", e.g. a URL that looks like this: https://www.website.com?utm_source=something&utm_medium=D2C=D2C. But that's an invalid URL anyway.