Hello UPSETLIN,
Welcome to Apple Support Communities. We want you to receive notifications properly, so you can stay alerted. Let’s see what might be happening here.
Do you turn on Low Power Mode on your iPhone? Since it reduces background activity and fetch settings, turning on this feature may cause the behavior you're experiencing. If so, please try disabling Low Power Mode, and let us know if that makes a difference. For more information, please check this out: Use Low Power Mode to save battery life on your iPhone or iPad
If you don't use Low Power Mode, do you recall anything changing on your device around the time this issue started? For example: Installing software updates?
Also, is this happening with specific contacts or all contacts? Does it happen when device is locked?
If you need help setting up an appointment at your local Apple Store or Apple Authorized Service Provider, contact Apple Support here: Get Support
We hope this information is useful. Kind regards.