Your router has likely changed the channel it uses for the 2.4 GHz radio. It's also possible your ISP has disabled the 2.4 GHz radio without telling you. That has been reported as being done by several different ISPs, mostly the cable companies.
The radio channel selection is usually set to Auto, so it can change channels if it feels there's an interference issue on the channel in use. The problem is there are 14 channels in the 2.4 GHz range, and Roku only supports 1-11. Because of channel overlap, there's really only three channels that should be used: 1, 6 or 11. Log into your router and see if you can manually set the channel used. Make sure the 2.4 GHz radio is enabled while you're in there. Just be aware that if your router is managed by your ISP (you rent it from them, or they gave you one for free), they might not permit you to make these changes. If that's the case, you have to call their tech support and ask them to make the changes. They can do it remotely, so it's not necessary for them to schedule a home visit (and associated cost).
Dan
Roku Community Streaming Expert
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