I have an Anet A8, and recently updated the firmware to Marlin 1.1.8. My only change was replacing the configuration files by the Anet A8 sample files built in with the firmware zip file.
Everything works fine but, sometimes, right after finishing a printing (while doing the "home all"), the LCD shows some weird data, like this:
The same happens when push the "confirm", after the mesh bed leveling.
I'd like to know why it happens. Is it a Marlin bug?
This is a known problem of the Anet A8 display, it is caused by electrical interference. Pressing the middle button will refresh the display.
This is prone to happen when doing long prints.
There are some reported successes of people inserting ferrite beads or toroidal rings.
No, this is not a firmware issue, this is a hardware issue.