I've had Rokus that stopped listing my wifi nets before. I haven't a clue what caused it but so far at least the following has always fixed it: I've found that when I've encountered wifi problems with my Rokus I've normally been able to solve them by restarting the router. After the router comes back up, restart the affected Roku (Settings > System > System restart) to start with a clean slate and try to reconnect. This makes no sense to me and I don't understand why it would work, especially since other wifi devices in the house connect well, but it has worked for me.
This has worked for some, not for others. Keep us posted.
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