devs refuse to fix bug: notifications are sent with priority = unknown. this defaults to 'normal' in the android os, and means new notifications aren't pushed through immediately when the screen is off and the device is in doze mode. other email apps use the priority 'high' so that notifications are immediate. old posts in the forum say it's been "escalated". if gmail devs refuse to change the default priority level, at least in the gmail settings allow users to force "high" priority on!