a3-a40 not sleeping - wakelock

If I fully charge my Iconia Tab 10 A3-A40 then leave it off (stand-by) after about 24 hours, the battery is completely dead.  If it's fully powered down, there is no battery drain.  If I fully charge and then use the tablet I get about 5 to 6 hours use before the battery is discharged. The problem seems to be that when in standby the tablet is not sleeping (no doze or deep sleep) and is losing about 5% battery ever hour.  I installed GSam battery monitor and it shows that if the tablet is left for say 10 hours (power button momentarily pressed, so screen off and should be in standby) that the tablet has been kept awake for the 10 hours, there has been no doze time and at most a minute of deep sleep.  Moreover, even though the WiFi is set to turn off during sleep it doesn't but stays on all the 10 hours.  The battery status doesn't update while the tablet is in 'standby' ie if it is at 98% when I put it in standby, then 10 hours later when waking it up it still momentarily reads 98%, then over the next few minutes falls precipitately to 50 odd % before resuming a more gradual discrharge rate.  If I install apps that force the WiFi off at screen off or force hibernation of apps (eg Greenify), then I get slightly less battery drain in standby, but GSam still shows that the tablet is 'kept awake' and still not deep sleeping.

I've tried clearing cache, completely factory reseting (4 times now) and installing no apps other than factory ones, and still get the same problem ie that the tablet won't go into dee sleep.  Without root, I don't know how to find/analyse what is causing the wakelocks.