Recently my Roku Ultra started to be invisible by the Android YouTube app. If I reset or do a "check connection" in my Roku Ultra, the YouTube app can find the Roku for about 5 minutes. This only happens on wired internet connection, if I'm using wireless, there are no problems.
I've tried a factory reset on the Roku Ultra, removing and reinstalling the YouTube app on both my phone and Roku, and powering down and up my router. Same thing happens, I can see the wired Roku in the YouTube app for about 5 minutes, and then it's give.
Any recommendations?
I really have not used the Youtube app very much at all with my Roku devices. (usually watching in guest mode is probably primary reason).
However, did just test with Android Moto Z (Android v.7.1.1) with ethernet connected Ultra 4660. The Youtube mobile app version was 17.34.35.
Everything worked and remain connected. Swapped between videos, etc.
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There may be either a compatibility issue with the devices and versions you are using, or the Android may be losing connection with the wireless network. Try using a different wireless channel in your router, or perhaps try connecting the Android to the 2.4ghz band of your network to see if that gives you a better connection. (May have to see if either the 2.4ghz band or the 5ghz band gives you different results or makes no difference).