EX7000 always disconnect

I am connecting my WIFI router R7000 with Ex7000 extender for a month

My wifi network always down everyday suddenly, some at holiday busy hours (i guess). And i needed to reset the router everyday.

i have checked with the ISP moderm, but all connected devices work normally.

I found out that the wifi extender EX7000 always disconnected with R7000,

my mobile can connected to EX7000 but EX7000 disconnect with R7000.

So everyday i need to reboot and reset the wifi extender.

for clash with other wifi router, i already chose DFS channel, but the problem remain the same

plx help