dimitris:

Supply the following if possible:

• Device problem occurs on
  Buffalo WZR 600DHP

• Software versions of OpenWrt/LEDE release, packages, etc.
  From 17.01.6: sysupgrade -f <backup.tar.gz> openwrt-18.06.1-ar71xx-generic-wzr-600dhp-squashfs-sysupgrade.bin

• Steps to reproduce
  Do the above sysupgrade. On reboot, WLAN is working (assuming it was configured to work before), but the WLAN LEDs are dark, leading to time wasted troubleshooting, re-flashing etc. It seems that what's needed is an extra default in /etc/config/system for this model:

config led
option name 'WLAN2.4'
option sysfs 'buffalo:green:band2g'
option default '1'
option trigger 'phy0tpt'

More detail in https://forum.openwrt.org/t/til-17-01-6-to-18-06-1-buffalo-wzr-600dhp-sysupgrade-with-config-small-led-nitpick/21282

Setting severity to Medium because of the potential for confusion and "destructive" action taken in response (flash without config, TFTP flash etc) thinking image upgrade is not "compatible".