Some ISP routers are incorrectly handling the speed protocols on the 2.4ghz band with their automatic management in some router firmware. By enabling legacy b, you are forcing the router to use all available speeds available to the network.
Could you tell me how one goes about changing the number on the router for AT&T please?
From this link, you can see how to change your gateway (router) settings for AT&T.
https://www.att.com/support/article/u-verse-high-speed-internet/KM1046172
Just select the appropriate router from the drop down menu for specific instructions. Basically, you will likely be typing http://192.168.1.254 into your web browser and then logging into your router portal.
If you have any more questions, feel free to post back and include your Roku model number (Settings/System/About) and your router model number as well.
So what’s the simple answer?
Welcome to the Roku Community!
Could you tell us more about the issue you have about the concern you're running into? We'd like to know more about how we can help! How long has the issue existed? In addition, can you please specify the exact steps you are taking to reproduce this issue so we can assist you further?
With detailed information, we will be better able to assist you.
Warm Regards,
Lianna