This happens randomly for some unknown reason. What has worked for many users is to start the setup from the beginning by pressing and holding the reset button for a minimum of 30 seconds, then instead of connecting to your home network connect to some other Internet source, such as a smartphone hotspot. It makes no sense, no idea why it works, for it has worked for many, many people.
Dan
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.