This is because the logout flow is synchronous, but sending a BLE message is asynchronous.
The fix would likely involve setting a flag, then when the login screen loads, inspecting the flag and sending the message.
Note that even though the message is sent, the phone will disable its hotspot automatically after a period if inactivity.
Currently, not setting this as M-61. We may bump this in priority later.
Comment 1 by khorimoto@chromium.org
, Aug 16 2017