You've mentioned social security and Marketplace insurance. While social security payments aren't taxable, they are considered for determining household income for insurance. When you underestimate income when applying for insurance, you have to pay back some of the subsidy.
Non-taxable Social Security benefits are counted as income for the Affordable Care Act and affect tax credits. This means that when calculating your eligibility for a subsidy your social security income is used to determine your eligibility and may affect the amount you qualify for
