I believe these unknowns are command line entries, in other words hacks. What happens is that a hacker using my computer accesses Gmail via the command line. Even Windows (the OS I am using to type this) has a Terminal that can access email using a command line.
You can see that the unknowns are using my computer because I use a VPN disguising my ip. The unknowns use the self same ip as I do.
The hacker is either not on duty all the time or can not be bothered, since the "unknowns" do not crop up every time I access Gmail.
Since I always use Gmail in the same way, the fact that sometimes there are unknowns and sometimes there aren't is pretty good evidence for the fact that they are hacks.
