You probably just exceeded the (MAGI) threshold for filing Form 8960.
See https://www.irs.gov/instructions/i8960#en_US_2024_publink10003905
Net investment income.
Generally, net investment income includes gross income from interest, dividends, annuities, royalties, and rents, unless they’re derived from the ordinary course of a trade or business that isn’t (a) a passive activity, or (b) a trade or business of trading in financial instruments or commodities. In addition, net investment income includes other gross income derived from a trade or business that’s (a) a passive activity, or (b) a trade or business of trading in financial instruments or commodities. Additionally, net investment income includes net gain (to the extent taken into account in computing taxable income) attributable to the disposition of property other than property held in a trade or business that’s not (a) a passive activity, or (b) a trade or business of trading in financial instruments or commodities.
