Steps to reproduce

1. Start the Minecraft Launcher on Linux while logged out of Mojang account
2. In this screen, ensure that "Keep me logged in" is checked:
3. Enter username and password as normal and select "log in"
4. Play the game as normal

Behaviour

After a certain amount of time (seems to be  around a day - possibly triggered by a system reboot, though I can't confirm this) I am logged out of my account automatically, despite having checked "keep me logged in"

I would expect that "keep me logged in" would keep me logged in for longer than that, and indeed on my old Windows machine I was almost never logged out.

Any idea what might be causing this?