This makes no sense to me, but it has worked.
The few times I've had Roku wifi connection problems, even when other devices connect without problems, have been fixed by restarting the router. After it comes back up, if the Roku won't connect, then restarting the Roku and re-establishing the wifi connection has always gotten me back in business.
- Roku Streaming Stick +, 3810X, Ser YH0059427035, wifi - Samsung UN55ES6100
- Roku Streaming Stick, 3600X, Ser 5S56D8240827, wifi - JVC EM37T
- TCL Roku TV 43S425/C107X, Ser X000001R60KV, wifi