I've had this happen several times in the last couple days. I play Factorio on 2 computers, lets call them A and B. After playing Factorio on computer A for a few hours I saved my game, exited, and put the computer to sleep. Several hours later I went to play on computer B, but I get an error message, "You are logged in on another computer already playing Factorio, launching Factorio here will disconnect the other session from Steam." At this point I should note that steam does not show me as playing any game. Clicking continue does... nothing. The Steam update window appears and says "Completing installation...%" (note: this is not the first time I've played Factorio through Steam on this computer) and stays that way indefinitely. I've experienced this both ways, A to B and B to A, and only with Factorio, never with any other Steam games. The solution I've found requires you to wake the other computer up, start Factorio, and exit it, then without putting that computer to sleep, start Factorio on the other computer. This doesn't seem to be an issue with Factorio per-se, but how it communicates with Steam, a process I am completely unfamiliar with.
*EDIT* just for good measure: task manager does not show any factorio-related processes running on computer A after waking it up, but the issue persists until Factorio is started and exited.
0.12.26 [Steam] Game already running
Re: 0.12.26 [Steam] Game already running
Could it be that you have to wait until the save(s) are uploaded to the steam cloud? Depending on your internet connection and map size this can take a while. That's the only thing I know of that is running on Steam after factorio.exe exited (evident by the fact it doesn't show up in the task manager).
Re: 0.12.26 [Steam] Game already running
I doubt that, because I had one computer running for about an hour after exiting, if it takes an hour to upload these saves something is still not right.
*Update* Exiting and re-starting steam on the computer that is locked out fixes the issue as well.
*Update* Exiting and re-starting steam on the computer that is locked out fixes the issue as well.
Re: 0.12.26 [Steam] Game already running
This looks more like a steam issue than Factorio issue, anyway, as you fixed it for you, I'm moving it to resolved.