I have several SNPs, but no evidence of disease. What gives?

This may be explained by phenotypic expression, which differs from genotype. Perhaps that patient has an excellent diet and lifestyle that minimizes the effects of the SNP. Many mutations also have low penetrance, meaning few individuals carrying that SNP actually exhibit consequences of the SNP. It could also depend on age or other factors: a younger person may not have had time for the sequelae to develop into measurable outcomes yet. You can read more here: https://ghr.nlm.nih.gov/primer/inheritance/penetranceexpressivity .