since the 3.5.388 update some of us have an annoying bug where all the apps are killed at night time even if they are in all the "white lists" and power optimization is OFF. So at night no more messages from Whatsapp, reminders, alerts (like MyPillbox). It doesn't happen with the system apps.
In my opinion it is due to the "nighttime extreme power saving" ZUK introduced that is not well managed and overcome any other setup.
I'm not rooted and looked.
Do you have feedbacks on this issue with the latest firmware?
I have DND mode enabled at night. But apps are still alive in the morning. I also get push messages from WhatsaApp. Experiencing some issues with push messages from Gmail and Threema but apps are not killed at night. Battery drains about 6-10 % at night with Spotify enabled for podcasts