We have had Roku Express for several years. One night it lost connection and is now not finding our Spectrum 5G network. It can see the 2G but is not letting us sign in. We have a new Roku Express just out of the box and is also experiencing the same issue.
Tried all the resets and scans. Even manually entering the 5G SSID but neither device is picking it up.
We have a Roku Streaming Stick and it is just fine - picks up the 5G network as well as our computers so I don't believe its the modem.
If you rent your modem from the ISP, some of them sent out updates recently that changed the 2.4GHz modes from b/g/n to g/n only. That knocked a lot of older Expresses (not to mention my parents' printer) offline. You'll need to login to the router and set it back to b/g/n modes.