According to the GL.inet debricking procedure, step 2, you can use either port for the debricking. Having gotten bitten by leaving it in the WAN port, I generally just use one of the LAN ports instead. The gotcha generally arises after the firmware has been flashed, and you’re still connected to the WAN port, wondering why you can’t connect to the LAN. I’m not even getting to the firmware re-flash page to begin with.
For the lack of any better option, I tried fiddling around doing the debricking procedure with the cable in the WAN port, then moving it to the LAN port once the lights have finished flashing. No, it didn’t make any difference.