Dr Bronners leaving residue, maybe?
I actually had a similar problem and asked the same question! My hair was sticky when wet, and looked kind of greasy when it was dry, even though it didn't feel greasy. My hair was soooo sticky when it was wet, it would stick to my skin. It was almost as though it had an adhesive on it. At the time, I was using baking soda and white distilled vinegar. I stopped using the vinegar, and my hair gradually lost the stickiness. I occasionally still use the vinegar, and after I rinse, my hair will feel slightly tacky. So at the moment, I'm attributing ithe stickiness to the white vinegar. I'm now using Dr. Bronner's and have no stickiness.