From Settings/Network/About are you seeing both an IP address and a MAC address? (are either of these all zeros).
From this same page, are you seeing a Wireless Channel and does this line up with the band you are attempting to connect to (either 2.4ghz or 5ghz)?
Finally, perform a Network Connection Test with the RokuTV to see what it is reporting. (Settings/Network/Check Connection). Press the OK button after test and report the speed results.
What is the router model number and the ISP (internet service provider)? May need to look into whether a firmware update for the router is needed, or if a firmware has been recently issued that is affecting the Roku.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660x, Premiere+ 3921, Express 4k+ 3941