Not receiving calendar alerts

I have calendar events set, some of which reoccurring every week or every day etc, with alerts set on “on day of event (9am)” or “2 days before” etc. everyday around 9am the alerts come through and I get a notification list of all events that I have that day. Recently this stopped and I stopped getting the notifications except for a few of them. I have an iPad and MacBook as well, but I have calendar sync off on those devices. How do I get my alerts back ?