It's sometimes accurate, but for instance, it will say certain players are online when they clearly are not visible anywhere on the map nor have they been online for days. In another example, it says I have been offline for 28 hours but clearly I am online since I'm the one screenshotting this. I then had one of my friends log in and it even further proves the defective feature for them as it shows them as being offline for 6 hours.
I rebooted the daemon and one player was no longer shown as online, but another was still shown online, despite the process being completely shutdown and restarted; there's absolutely no socket in use for the user that is shown as online.
In case it matters, yes I am aware the last online time is relative to the map's progression in time, not real world time; if the map is paused, time will not move forward for the last online column. However, clearly there's an issue with it showing some users as online or not.



Factorio server version 0.17.54
Linux kernel 5.1.12-300.fc30.x86_64