Slate AX and Opal network problems

I am using GL-AXT1800 Slate AX as primary router (connecting to WAN) and GL-SFT1200 Opal as secondary router (connecting to Slate AX via cable). As the Opal is a replacement of my old router, some problems come out after the replacement, where Slate AX - old router network don’t have such problems

  1. Connected to WiFi but no network
    Several phones in my home, when taking back phones to home or booting up the routers so that those phones “meet” the routers SSID, always connect to WiFi but no network. So I need to switch off and on the phones WiFi for reconnecting in order to connect to network, that is annoying.

  2. Connected to router but no network
    My PC connect to Slate AX via cable. When booting up my PC, usually my PC cannot connect to network either. So I need to unplug the LAN cable and plugging in back in order to connect to network, annoying.

  3. Slate AX sometimes crash
    LED on Slate AX sometimes flashes and the whole network crash. Need to reboot it several times for recovering.

Slate AX is in version 4.5 firmware, what I can do to solve these problems?