Note s does not enter sleep mode

I go my Note S yesterday and started learning its capabilities. I registered it to use Play store, and downloaded Gmail, Gboard and Gdrive.

For some reason, after a day of usage, the device stopped going to sleep, even when I set it to sleep after 3 minutes of inactivity. Could it be that one of the apps keeps the device awake? I already tried rebooting, and the problem persists.

I do not use a cover yet, but keep the device in its original packaging.

Update: after removing Gdrive the problem disappeared. Is this a known issue? What is the recommended method for syncing the device using wireless?