No calendar notifications from old phone events after switching phones

I recently switched from a Wiko LENNY (don't laugh, it was my first phone) to a Samsung Galaxy S7. When I tested notifications at first they seemed to work, but my phone keeps missing events. I've come to the conclusion that __I only get notifications for events created on the Galaxy but not for those created on my old phone__. I currently have both the Samsung and the Google calendar app installed on the Galaxy and both behave in the same way (either both or neither send a notification). I also made sure that "Notify on this device" in Google Calendar is checked. I can see all the events I missed on my new phone (so the cloud syncing must have worked) and they all had notifications set for them. In fact, when I boot up my old device __I DO get notifications for all the events I missed__ via the built-in calendar app. So: How can I receive notifications for events created on my old out-of-use phone on my new phone?