L3 boards are easy to deal with when you are aware of just a few things.
When flashing (with loadfw.bat under L3_yymmdd.zip) or updating settings (with JigOn), make sure:
1) L3 board is directly connected to PC's USB
2) There is just one L3 board connected to the PC
If the board is in weird state (not recognized as "L3" device or does not work with the latest firmware update or JigOn)
1) Boot into bootloader (press/short ~ and connect USB, "HIDBOOT" device gets recognized)
2) Run loadfw.bat under L3_FW_RESET.zip
Occasionally, bootloader/firmware are blown due to static electricity or voltage spike from faulty components (especially RGB LEDs), MCU needs to be reprogrammed via ISP loader physically connected to the board.
I haven't seen this being done on GH, so it would be really handy to have someone local (familiar with this sort of things) come up to speed. If you need the connector (looks like this
http://kbdlab.co.kr/index.php?mid=board_CDST33&document_srl=3854117), make one or talk to someone on kbdlab. My guess is there are fair number of PCBs with blown bootloader/firmware floating around.
If MCU reprogramming doesn't fix things, most likely you are dealing with component failure. This is beyond typical DIY territory, so your best bet is to talk to the GB runner or local guru.
IMO, L3 boards and software are proven with years of track record. It's easy to solder and utilities are all self contained. There are idiosyncrasies like JigOn UI and limited hub/multi device support, but most people don't flash/update their keyboards often.