I believe this is related to the problem where the keyboard MCU sometimes (rarely?) spontaneously resets while in deep-sleep. Depending on your luck (there’s a missing pull-up resistor on the original keyboard), the keyboard will either drop into DFU mode (which presents as “can’t turn laptop on despite batteries being charged, until resetting the keyboard, or replugging the keyboard, or replugging the battery packs”), or, it will reset normally - displaying the logo, and, I think, never removing it (without user intervention) or going back into deep sleep mode. I looked into this in this problem in some detail on this thread (though not considering the logo aspect), with some patches (that are in the latest firmware) that should at least help to minimise this problem.
So this could result in such burn-in if you leave your Reform plugged-in (to prevent the stories of woe from over-discharging the batteries), but unattended and lid-closed for long periods.
I’m currently looking at the keyboard firmware again for some other changes, but will also try to address this problem - specifically, making the logo go away automatically after ~1 min, and/or double-checking that the MCU goes back into deep-sleep (clearing the logo on its way) after inactivity.