Any other security (related) software installed ?
I don’t know if it is the case with the S6, but many mobile devices come standard with a av and/or anti-theft.

  • If there isn’t any other security software installed, remove anti-theft and AMS and install it from scratch.
    https://www.avast.com/faq.php?article=AVKB166
  • Visit https://my.avast.com and remove the device from your account.
  • Install AMS and do not make any changes to the settings.
  • Connect the device to your account.
  • Install anti-theft and do not make any changes to the settings.
  • Visit the site and check if it shows that AMS and anti-theft are installed.
    It can take a bit before everything on the site is updated.
  • Try the locate command and see if it is working

Let us know if is working or not.