It's interesting to see that many users have issues with the 5 GHz wifi, and it's quite confusing how many threads we have for this device by now...
So I assume this is the fix that worked for you:
Could you check whether the problem might be related to the position of the art calibration data? I recall summarizing the issue before in this post:
So I'm wondering what is the output of hexdump -s 0x5000 /dev/mtd9 for your device, maybe we already found two solutions to the same problem
One of my devices says
H/W Ver.: C3 F/W Ver.: 3.10EU
S/N: SY6A2IA00XXX
on the label, and 5 GHz works out of the box with the current snapshots, so it seems they changed something to the mtd layout after that. This should definitely be fixed... (but currently I'm still hoping I could eventually finish rewriting image encryption in C this weekend )
)