I've also had this issue. Another app besides missed notification reminders that can be used as a workaround would be "alertify". This app lets you set a notification sound for not only an app but also for specific key words in the notification. You can then go into the apps settings and set the alert type to "alarm" instead of "notification". Now notifications handled by the app will use the alarm algorithm (audible in headphones, bluetooth, and phone speaker). You may have to manually set the do not disturb schedule in settings of the app however, as alerts will no longer follow notification rules but alarm rules, which alarms are not suppressed by the devices do not disturb schedule. Also if you need to silent notifications you'll need to change alert type back to "notification" in the app so that they are silent when you turn the volume all the way down on the phone.
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