Funny timing. Two days ago I had a display issue again after accidentally leaving the laptop on battery and finding it turned off. Neither port would work, both with GET_CABLE_PROPERTY failed (-5) at boot time and then nothing in dmesg when plugging/unplugging display cables. This time, putting a random USB device in each port (back left and center left) through the USB-A adaptor woke them up or something and then the displays worked again. Sounds quite similar…