SOLVED: I have been in contact with a Ubisoft agent who told me that the problem is caused by game sharing apparently "Ubisoft currently does not support game sharing" and you will either have to play on the account which made the purchase or buy the content for yourself. Luckily I was able to refund my gold edition of Watch Dogs Legion then purchase it again on the correct account and the content is now showing up.
Thanks for getting back to us with that information, ruebenvader. At this point, I'd recommend getting in touch with our technical support teams, either over our website or on Facebook or Twitter. They'll be happy to look into this missing content further with you. Please also make sure you have your receipt for the Season Pass ready to provide to them.