I just successfully started with NC15 on a synology NAS. 2FA also worked with a PC/browser session authenticating the iOS login (before setting the device password - then this seems no longer needed) but when trying to authenticate a browser access from my PC it seems the iOS device will receive the 2FA message only if it is not active. The iOS device shows the 2FA message reliably but only if I unload the app first, then initiate the 2FA login on the other machine, then load the iOS app - now the bell symbol will have the message and I can slide / activate the login.
Not sure this is iOS specific or a bug - but maybe it helps somebody here and maybe (2) somebody has some ideas or suggestions?
Happy New Year btw!