Go to settings --> advanced settings --> battery manager --> protected apps, then find Life Reminders, and protect it. This is "whitelisting" the app so Huawei's overeager software doesn't shut it down for no reason.
Go to settings --> apps --> advanced --> ignore battery optimizations, then find Life Reminders and ignore it. Don't be tricked by the misleading wording, "ignoring" the app actually means to let it run, because you're telling the battery optimization function, aka Doze, to "ignore" that app.
Go to settings --> notification panel & status bar --> notification center, then find Life Reminders, then activate "allow notifications" and also "priority display". You have to activate the priority part too to make sure you get notifications. I've tried just activating allow notifications but not priority and I still didn't get notifications from Life Reminders.