You could try that or try hard resetting both the TV and router and set both up as new. If you could get a network cable and try that and see if the Roku still has issues. Sometimes a hardwired connection will straighten out a wi-fi issue.
You could also try the other suggestion at using a different wi-fi channel as that frequency may be too crowded. I would suggest before doing that though is download a wi-fi analyzer app and scan to see if the network channel your router is using is too crowded. Most routers manage themselves, but sometimes that fail to do so, if a network got crowded after initial setup.
It is possible that it is a hardware/firmware issue of the Roku as Roku always is updating/changing the OS, so it is possible there is something going on there. There should be an upcoming firmware release coming soon, so that might fix it.
I have seen a similar issue with identical devices at my home that had no explanation either and I was sure it was something with the device too, only to figure out later that a router firmware update that was released sometime later fixed it. That seems to be a common issue with newer model routers.
Try disconnecting/unplugging your extender as sometime an extender can cause issue as well, as devices can struggle to figure out which network device it should connect to. If you have an area that is seeing both the router and extender and are too close together, that could potentially cause issues.
Wi-fi is a bit quirky sometimes as it is subject to interference and can be interfered with by various things in and outside the home.
