Birthday alert not working

Hello everyone,

I have recently gotten my first iPhone (7, iOS 10.2) and am so far pretty happy with it. But somehow I can't get the birthday alerts to work properly and can not find anything about that problem.

I use gmail and have synchronized my contacts with my personal google account and my exchange account from work. Everything except the alerts works fine:

- All contacts are in my contact list - including their birthdays (day, month and year).

- In the calendar options i have turned off the gmail internal birthday calendar and turned on the birthday calendar found under "others", which to my knowledge is the calendar provided by the contacts app.

- People's birthdays are displayed as such in my iPhone calendar (including the little birthday present symbol).

- I get notifications from calendar if I there is an event with added notification.

- In settings I set the "Default Alert Time" for birthdays to 9 a.m.

I have already rebootet my phone and tried setting the default alert time to the day before, but I still do not get a single alert for birthdays.

Does anyone know this problem or know how to fix this? This somehow really anoys me.

Best regards

Matthias