If you are getting an update when trying to manually update from About then run in ADB Shell the following commands:
The first two commands are root commands. So if they don't work is normal. We are just testing to see if your device still responses to root commands.
You might get an error on the first or second command since you say you are not rooted anymore.Code:
pm enable com.amazon.device.software.ota
The following commands work without root.
pm unhide com.amazon.device.software.ota
cat /system/build.prop | grep number
What number does it report after the third command ??
Permission Denial: attempt to change component state from pid=3698, uid=2000, package uid=32011