As with most of these Express issues, you are going to have to make sure that the 2.4gz band of your router is configured properly for both the Roku to connect and use the internet.
Almost every modern router is dual band. They have a 2.4gz and a 5gz band. Some devices operate on the 2.4gz band and other devices (dual band devices like cell phones and newer laptops) can operate on either the 2.4gz or 5gz band and can even jump between the 2 bands to maintain connection.
The Express only operates on the 2.4gz band. Provide your router info (model) and ISP provider and can provide some troubleshooting that you will have to do to verify and change router settings as needed.
Depending upon how much control your ISP has over your router settings, it is fairly easy to change yourself after you login to your administrative panel.
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