It looks like AVR is not able to switch the LCD backlight on immediately instead alternating between on/off or high/low brightness levels.
This needs to be investigated.
This happens because my AVR driver allows writing the BL/LED registers while the device is in LPM. It looks like the firmware of the controller is first setting the backlight status then WHOOPS realizes it is in LPM and turns it off again. The number of flashes depend on the number of sysfs LED brightness file updates.