i was able to login after a few attempts last night.
the problem is with mom's account. yes bank keeps on forcing password changes. and i have lost track of her password. until now i was able to just login using fps. to re-register, i would need either login details or debit card. her debit card was replaced recently, but i do not think i got around to setting its pin. without app, setting pin is going to be annoying. without pin, i would not be able to login. basically creates nuisance for me.
best option is that the app is not updated right now on her phone. i reset her debit pin to something i note down or remember. and then re-register her when the app updates and kills the registration.