Network - Wireless & Wired Connections

[renojim]

If that Xfinity router is 5GHz only (which would be unusual) then your 3900X won't work.  It probably also supports 2.4GHz, but they may not have enabled it because all ISPs seem to be idiots.

[atc98092]

The 3900 is a single band device, and doesn't support 5 GHz. If you can log into your router, see if it has a 2.4 GHz radio that is disabled, and if so turn it back on. Otherwise, yes you need a Roku with dual band support, such as the Stick, Ultra or one of the sound bars. 

[Dragoonrl]

You ha e to totally reset your roku from scratch.  It must be a bad update.  After I set everything back to default and reset it worked fine.

[Dragoonrl]

Reset your roku to factory settings and restart.  Must be a bad update.  It worked fine after I did this.

[JackN777]

If you folks can access and adjust your WiFi routers, then try forcing it to use 2.4 GHz channels 1, 6, or 11, instead of auto.

Worth a shot...