The relatively strong performance of mortgages in vintage non-agency MBS could be disrupted by interest rate resets and the expiration of interest-only periods, according to analysts at Fitch Ratings. Roughly half of all performing first-lien mortgages in non-agency MBS will be exposed to monthly payment increases during the next five years, Fitch said in a report released this week. The rating service determined that if a borrower’s monthly payment increases by 35 percent, the probability of default for the borrower doubles. “The product that’s going to be most affected is...