When error reporting is turned on, CB integration is activated and avatar is set to CB there are warnings produced in the ajax fetch of the user avatar.
The problem is that there is no check to see if $avatars[$key] exists. This produces warnings and thus breaking the json returned by the ajax call.
To fix change line 50 in com_hotspots/models/users.php to :
$users[$key]->avatar = ( isset($avatars[$key]) ) ? $avatars[$key] : '';
Kind regards,
Tom