Hi Sum
Disability Rights Handbook edition 50 states on page 109 (6) last paragraph states, "Your entitlement to the lower rate is protected if your universal credit award is terminated and a further award made because you cease to be, or become, one of a couple and if you come off UC for up to six months because your income (or joint income) is too high."
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems