Wifi clients forwarding drops unexpected

Hi, everybody.
I have a Keenetic Omni router with installed LEDE Reboot.

root@LEDE:~# cat /etc/os-release 
NAME="LEDE"
VERSION="17.01.2, Reboot"
ID="lede"
ID_LIKE="lede openwrt"
PRETTY_NAME="LEDE Reboot 17.01.2"
VERSION_ID="17.01.2"
HOME_URL="http://lede-project.org/"
BUG_URL="http://bugs.lede-project.org/"
SUPPORT_URL="http://forum.openwrt.org/"
BUILD_ID="r3435-65eec8bd5f"
LEDE_BOARD="ramips/mt7620"
LEDE_ARCH="mipsel_24kc"
LEDE_TAINTS="no-all"
LEDE_DEVICE_MANUFACTURER="LEDE"
LEDE_DEVICE_MANUFACTURER_URL="http://lede-project.org/"
LEDE_DEVICE_PRODUCT="Generic"
LEDE_DEVICE_REVISION="v0"
LEDE_RELEASE="LEDE Reboot 17.01.2 r3435-65eec8bd5f"

Some times in any moment all mobile devices connected by Wifi lost internet connection. Devices still stay connected to Wifi and LAN, but no packages can go outside. But devices connected by wire (Smart TV, laptop) works fine.

root@LEDE:~# sysctl -a | grep forward
net.ipv4.conf.all.forwarding = 1
net.ipv4.conf.all.mc_forwarding = 0
net.ipv4.conf.br-lan.forwarding = 1
net.ipv4.conf.br-lan.mc_forwarding = 0
net.ipv4.conf.default.forwarding = 1
net.ipv4.conf.default.mc_forwarding = 0
net.ipv4.conf.eth0.forwarding = 1
net.ipv4.conf.eth0.mc_forwarding = 0
net.ipv4.conf.eth0.1.forwarding = 1
net.ipv4.conf.eth0.1.mc_forwarding = 0
net.ipv4.conf.eth0.2.forwarding = 1
net.ipv4.conf.eth0.2.mc_forwarding = 0
net.ipv4.conf.lo.forwarding = 1
net.ipv4.conf.lo.mc_forwarding = 0
net.ipv4.conf.wlan0.forwarding = 1
net.ipv4.conf.wlan0.mc_forwarding = 0
net.ipv4.ip_forward = 1
net.ipv4.ip_forward_use_pmtu = 0
net.ipv6.conf.all.forwarding = 1
net.ipv6.conf.all.mc_forwarding = 0
net.ipv6.conf.br-lan.forwarding = 1
net.ipv6.conf.br-lan.mc_forwarding = 0
net.ipv6.conf.default.forwarding = 1
net.ipv6.conf.default.mc_forwarding = 0
net.ipv6.conf.eth0.forwarding = 1
net.ipv6.conf.eth0.mc_forwarding = 0
net.ipv6.conf.eth0.1.forwarding = 1
net.ipv6.conf.eth0.1.mc_forwarding = 0
net.ipv6.conf.eth0.2.forwarding = 1
net.ipv6.conf.eth0.2.mc_forwarding = 0
net.ipv6.conf.lo.forwarding = 1
net.ipv6.conf.lo.mc_forwarding = 0
net.ipv6.conf.wlan0.forwarding = 1
net.ipv6.conf.wlan0.mc_forwarding = 0

The same issue was also when I used OpenWRT firmware.
Can somebody give an advice, in what direction should I dig?