The WiFi routers will rarely need a reboot. They will also not "disappear" for some devices, but not others. This is an issue with the devices themselves.
The first thing to try, is to reboot the device.
If rebooting the device does not work, then you might need to make the device forget the network and manually add it back.
If this doesn't work, then the next step is to reset the network settings.
For Apple devices:
Reset your Network Settings.
Go to Settings > General > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you've used before.
For Android devices:
Find and tap Settings > System > Advanced > Reset options > Reset network settings.
For Windows 10 devices:
To reset network settings, go to Start menu > Settings > Network and Internet > Status > Network Reset.