*I in no way am saying keep your phone open to vulnerability, just saying this will help *possibly* make your phone easier to root once we do figure it out. *
Go to developer options and uncheck the option marked "auto update system"
You will of course get the persistent update notification if you are past the point of being able to stop it with package disabler.
If you can still use package disabler, just disable com.wssyncmldm and it will remove the notification.
And when the thing pops up without the option to install update later, just press the back button and it will disappear
Just trying to help those of you that don't want to keep updating