I did extensive search and found no fix so far.
Problem: if my phone is locked for maybe 10min, then it will not display notification for incoming Signal, Whatsapp and Google Voice messages, until I unlock the screen and run the apps. In other words, I will not get notified of new messages if the phone is locked for over 10 minutes.
Native Messenger app is not affected, it displays incoming message right away. Gmail is good too.
I do not use Wifi, it is turned OFF. I am on Data 100% with T-Mobile. Stock ROM, rooted with Magisk and TWRP.
I have done "Battery Not Optimized", "unrestricted data", Battery saving mode is set Never, and there is no battery saving apps installed such as Greenify etc.
I have removed and reinstalled these apps from Play store, cleared data and cache, the whole 9 yards.
Still stuck with delayed notification.
Anyone with suggestions?