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.
Canara Bank has the worst app. After every normal update they require to sim verification, setup pin, debit card details for account authentication. Doesn't matter if you remember your old pin and nothing is changed.