Roku Does Not Stay Connected to WiFi

zorro54-  expanding on RokuKariza-D 's reply ....

There are a couple of network connection problems recently being reported that have been caused by updates to routers. These have primarily been reported with routers supplied by internet providers, but it's possible they could also occur with user-owned routers that have received updates.

• ROKU LOCATES NETWORK BUT CANNOT CONNECT
  Some router updates have changed the router's security setting from b/g/n to just g/n, causing some Roku models to lose their ability to connect to the network. The solution is to set the router's configuration back to using b/g/n security.
  
  
• ROKU CANNOT FIND LOCAL WIFI NETWORK
  Some routers (reported from Xfinity and Cox, but there may be others) have had their 2.4 GHz WiFi band turned off, leaving only the 5 GHz band operational. Devices with single band WiFi radios, notably Roku Express and Premiere models (but not Express 4K models) as well as many other single band devices can not even see the 5 GHz band. The solution is to reconfigure the router and turn the 2.4 GHz band back on.
  
  If this problem was not caused by a router update deactivating the 2.4 GHz band, often a restart of the router (even if other devices are still connecting) followed by a restart of the Roku via Settings > System > System restart (for Roku TV it's Settings > System > Power > Restart) will allow the connection to be reestablished.

If you need to make configuration changes on equipment supplied by your internet provider but you have no access to its settings, you may need to request your internet provider to make the changes for you.