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Make sure all your devices are signed out. Check the user Devices and registrations overview in the portal for any device registrations. If there is no logout recorded on an device, logout this device (do note that a No logout recorded can be set to an older version, this is correct if a newer version is installed).
If Skype for Business is running in the background on these phones, users will receive push notifications as long as the session expiration interval has not expired. The mobile device must send a notice to the server indicating that the device is still active before the session timeout is reached. If it does not, the device will be listed as inactive and the user will have to log back on to the system. On iPhone and Windows mobile this happens after 1 day. On Android this happens after 1 hour.
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