Devices that connect one night and the next morning cannot are usually tied to the router making an automatic channel change. If they are a 2.4 GHz only WiFi device, the router probably changed the channel to 12, 13 or 14, which are not supported by Roku devices. On 5 GHz, the channel might have changed to what is called a DFS channel (49-148), which also are not supported by Roku. So the first thing to check is the router channel assignment. Most likely you'll find it set to Auto, so you need to manually change the channel. On 2.4 GHz, use channel 1, 6 or 11. For 5 GHz, use channel 48 or lower, or 149 or higher.
This is all assuming your router isn't even shown on your Roku. If it's listed, but you can't connect, the next likely problem is the 2.4 GHz radio set to Mode G/N. Many routers and cable modems have issues on Roku devices in that mode setting. Instead change the Mode to B/G/N. If you are renting your router/modem, you might not be able to adjust those settings yourself, and will instead need to your your ISP's tech support for assistance.
Dan
Roku Community Streaming Expert
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