N5 Google Now reminder notification settings bricked

I've a N5 16GB on 5.1.1 and I've started facing this issue recently. Few weeks back my notification sound for Gnow automatically switched itself to 'silent' with vibration ON. Since then I've tried multiple times to switch it to a different tone but to no avail. As soon as I refresh my Gnow cards the settings switches back to 'silent + vibrate' mode :(

I rebooted the phone in safe mode to check for any bloat ware but still got nothing to blame. I don't know what went wrong. PLEASE HELP.