Generally I find that restarting the router fixes this.
Sometimes I have to restart the Roku.
Very rarely, I have to unplug the Rokubfitprva minute or so then plug it back in
- 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