Unknown addiction [closed]
Idiopathic: Of unknown cause.
Idiopathic specifically relates to disease, which addiction certainly is considered.
I'm not a medical doctor, but I have come across the term undiagnosed condition. It is used in the following sense:
An undiagnosed condition is one where someone experiences symptoms but does not have a formal diagnosis. - Brain and Spine Foundation
Undiagnosed conditions can also be asymptomatic. The links relate more broadly to physical and mental health, but the ideas are consistent with what you have described.