None of my Rokus have an Ethernet port, so I've never tried this with a wired connection, but I've had success with wifi connections, even when all other devices in the house have connected okay, so it might be worth a try:
Restart the router.
Restart the Roku.
When both are back up, try to reset Roku's network connection.
It frankly makes no sense to me, but it has worked for me on several occasions when mere restarting of the Roku didn't cut it.
- 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