Just updated mine from RC1 and then figured out that there is no usable 5GHz radio.
The problem is: radio0 which supposed to be 1st 5GHz becomes "Generic Unknown" and not possible to enable. radio1 is 2.4GHz so everything alright; While radio2 is another 5GHz showing "Marvell 88W8887 802.11ac/b/g/n" can only be set with channel "Auto" (anything else will disable it) and system defaults it at CH 149. Even with 149 my clients can not use it at all.
One major difference though, UK and FR are both collated under ETSI regulatory rules (yes, the UK has been diverging recently, but the old Marvell firmware doesn't know that - and none of those differences matter much to the 2.4/ 5 GHz radios in those Marvell routers anyways). Japan/ MKK is considerably different though, with quite different allowed channel maps.
The regulatory settings for all radios must match and be correct for your region (achieving that might require removing the mwifiex kernel modules, as that radio is hardcoded to FCC).
Reset the router to default, still observing weird thing.
Radio0 is 2.4GHz, nothing special and fully functional.
Radio1 is 5GHz, Auto channel selection always 149 DFS (why?), but even I tried to connect it, the speed is only about 20-30Mbps.
The second 5GHz radio disappears (I suspect the above one is the one we shouldn't use but there is no more 5GHz radio now)
#hacked from /lib/upgrade/linksys.sh
cur_boot_part=`/usr/sbin/fw_printenv -n boot_part`
if [ "$cur_boot_part" = "1" ]
fw_setenv boot_part 2
fw_setenv bootcmd "run altnandboot"
elif [ "$cur_boot_part" = "2" ]
fw_setenv boot_part 1
fw_setenv bootcmd "run nandboot"
# re-enable recovery so we get back if the new firmware is broken
fw_setenv auto_recovery yes
@anon79208902 - Hardly a piece of junk, just mwlwifi is a borked piece of s***
No I won't, even the WiFi might be a bit bad to use, I would still want to use it as a wired router due to it's speed, as well as expansion option, I can connect a 4-bay eSATA tower to it to act as an entry level NAS.