I triple the buffer size as @KONG recommends and it works fine.
Copy and paste these commands at the same time in your SSH client and maybe the problem will be fixed:
# Increase the buffer size in nlbwmon
uci set nlbwmon.@nlbwmon[0].netlink_buffer_size="1572864"
# Increase the maximum socket buffer size
sed -i "/^[^#]*$/d" /etc/sysctl.conf
cat << "EOF" >> /etc/sysctl.conf
net.core.rmem_max=1572864
net.core.wmem_max=1572864
EOF
# Saving modified values
uci commit nlbwmon
/etc/init.d/nlbwmon restart
sysctl -p