Help & troubleshooting for network issues, including connecting your device to your home Wi-Fi network, connecting to public networks, troubleshooting wireless issues & ethernet connections, and optimizing streaming performance.
The Express only supports the 2.4 GHz band, so it won't see any 5 GHz access points. Since there appears to be a number of nearby access points, it's possible that they are interfering with yours. I'd first suggest trying a different channel in your wireless router. It's probably set to Auto, so you would have to manually choose a different channel. Also, make sure your SSID is being broadcast. That's another setting that can be toggled in the router.
Since it worked on initial setup, it's possible that none of this is applicable. But it's worth a shot. I will add that I bought an Insignia Roku TV a few years ago, and after the initial setup and update it got stuck in a reboot loop and I replaced it as defective. Yours too might just be a defective player, and in that case you should be able to exchange it. After I exchanged my Insignia TV, the replacement worked without a problem.
Dan Roku Stick (3600), Ultra (4640), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.