Employers late in providing information on wages

Our client works part-time regularly and wages do not vary. This month her employer was late in providing the information.  Universal Credit have assumed a large amount for earnings, leaving her with a partial payment of her Housing Costs, and no other payment.  Does anyone know what happens now?  How soon will they be able to put this right?  Is there a danger that they will use the date of notification rather than the dates covered by the wages when they assess her income for the next monthly period, and have two wage slips to deal with?

https://www.rightsnet.org.uk/welfare-rights/caselaw/item/secretary-of-state-concedes-that-where-an-employer-fails-to-notify-earnings

Thanks, that’s really helpful.