Thank you for your reply! I went and checked my rokus... one is the Express 3960, but the other was a 3930. I disconnected that one, tried again with the 3960, and it worked! It's picking up the 2.4 ghz network, but whatever. All of our hardwired devices and phones and tablets are running on the 5ghz, so it's all good. Went out and bought another Express 3960 (totally worth the $29 if it means I don't have to call mediacom again!) and now we're up and running. Thank you!
Just to clarify a few things (just for your own information/knowledge).
1. Wired devices do not use either the 2.4gz or 5ghz bands. Those are wireless/wi-fi bands. All wired devices communicate through an ethernet protocol. You can turn off both your 2.4ghz and 5ghz radios in your router and your wired devices would continue to work on your network.
2. Roku devices are working on the 2.4ghz band only. Likely, the MediaCom setup is configured in a mesh-mode (website shows they are issuing Eero routers), so either the router is determining the best band for connection of your Roku devices is the 2.4ghz band, or the 5ghz band is configured to use DFS channels (wireless channels on the 5ghz band numbered 52-140) that are incompatible with Roku. Roku can only see and use non-DFS channel 36-48 or 149-161.
Nothing wrong with using your Roku devices on the 2.4ghz band. If however, you ever feel the need to use 5ghz with your Roku, you will either need to contact MediaCom to disable the DFS capability, or you can do it yourself through the MobileCare app or login to your MediaCom account. Looks like their Support Page takes you to their Youtube page for videos on making some changes. Just hover over Support in their navigation menu at top and you will see "How-to videos".
Just mentioned the above to keep in mind in case you run into issues in the future. If everything is operating correctly and you are satisfied, then I would leave your setup as-is and just enjoy your Roku devices. 👍
Roku Community Streaming Expert Just another Roku user... I am not a Roku employee. Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102