The TEST notification in aCalendar notification settings should detect this and guide you to power saving settings, which need to be changed.
This is a Huawei firmware bug introduced with EMUI 8, that is blocking the broadcast of due event notifications, against the Android specification (ACTION_EVENT_REMINDER should be whitelisted).
You can enable this as Sticky Date in notification settings. This should also fix the bug with Huawei devices delaying all-day notifications by 9h to fix a bug in the Huawei calendar app.
Also see https://dontkillmyapp.com/huawei for additional Huawei-specific settings which might affect normal app functionality.