iOS does not allow more than 64 notifications per app. For this reason we recommend setting max 6 Check-in reminders per day. Please note setting more than 6 per day will have unexpected results (i.e. reminders can stop working suddenly and start working again after a few days). Currently the app allows up to 20 notifications per day and with the next update we’ll set a hard limit to 6.
In case you don't have more than 6 checkin reminders set per day and still not receiving notifications, please check the following article: I am not receiving any notifications!