WiFi has to be rebooted each time for connection

I have 2 WiFi routers in my house. one of them is a modem + router, the other one is a spare I had. I configured the spare as an extender on the WiFi network to expand the reach. Basically, now I have 2 WiFi networks in my house, where the second router is connected to the main router through a CAT6 cable.

The problem is that each time I have to reconnect certain devices, like my laptop or my Google Home device, it shows "No Internet". After WiFi restart, the first time I connect the device it is fine, but say, if I put my PC on sleep mode and then reconnect, this problem arises. Same with the other devices too. This problem does not arise with mobile devices.

I'm more or less a newbie in these matters, and followed this tutorial to get it done. I have a very basic understanding of these things and would really appreciate some help from the pros xD.

Thanks in advance.