ISP ppoe problem

Hi all
i have a problem with my ISP
my clients have SXTsq 5 High Power with station mode and plugged TP-Link TL-WR840N 300 Mbps Wireless
when they turn off power from both ( Mikrotik & Tp-Link )
they cant access to internet but when they unplug the Wan port then plug in or they reset default the wireless router the internet will come back