Wi-Fi stops working for separate devices

There is one router in the house and it's coected to the TVs via cable and has Wi-Fi. Occasionally one of the devices coected will lose the coection. For example my phone will stop getting the WiFfi from the router, but the laptops and the TVs will work fine. Or only one TV loses the coection and everything else can still use the Wi-Fi. Restarting the wireless client device doesn't work. The only thing that can fix it is restarting the router itself. This is the second router that we've been provided with and the same thing still happens. What could be causing it?