Is the Hang Seng bank app this one --> https://play.google.com/store/apps/details?id=com.hangseng.rbmobile ?freeze it and it doesn't work either. It works in all banks except one. My mobile has Android 12 (Miui 13), when I had Andorid 11 (Miui 12) I had the same problem but solved it using the magisk 23. Magisk 23 does not work on Android 12 , I read that some block URLs with Adaway but there is not much information about it
I tried it yesterday and confirmed that it stopped detecting root when the Magisk app was not enabled. Make sure you clear the app's storage and kill it first before opening it again.
I'm using Stock Android 12, Magisk stable with USNF and Shamiko modules.
I don't think Adaway would help, because it is just for blocking ads.