There is an advanced wifi setting in our device. ie, if the wifi network is slow or unstable, the device will disconnect the wifi and use the mobile data instead. Here it is asking wheather to disconnect wifi or keep connected to wifi (because your device might detected some issues with that network)
So if you choose "Keep wifi connection" then it will not ask about it in the future. If you choose disconnect, then the device will automatically disconnect wifi whenever it detects an issue.
So my advise is, 1) If this current network is your home/office that you use daily, then tap "keep wifi connection" , 2) but if you have unlimited mobile data, i think it'll be better to choose "disconnect" to ensure your data usage without interruption. 3) If you are not a mobile data user or you have very restricted usage, please turn off the advanced feature. (Settings > Connections > wifi > three dots > Advanced > Switch to mobile data > OFF.) Hope that helps. Thank you.
