As nobody else has replied I will, although I don't know how useful I will be.
I have used the Santander app today without problem, paying the gas engineer but I don't have a mortgage account - I don't know if that is a separate app.
the app is working fine for bank accounts. The website is also working fine for bank accounts. You cnt do the mortgage via the app, but thewebsite wont do the mortgage like it normally does.
#Thanks for your help barry