I have an iPhone 4 running iOS 7.1.1 and as soon as my iPhone enters the lock screen the network connection to the SanDisk Wireless Flash Drive is dropped and any media playback that was in progress stops. What this means is that you need to keep the screen active (on) while playing any media files which shouldn’t be necessary as it just runs down the battery on the iOS device.
Note that other network apps don’t have this problem. For example, you can enter the lock screen (turn the iPhone display off) while streaming over either WiFi or 3G/LTE when using services and apps like Pandora and Amazon Music. It seems like the SanDisk WFD app and device should be able to do the same.
Is this something that will be fixed in a future app or firmware update? Without this change the Sandisk WFD can run the battery down on iOS devices much more quickly than it should (when streaming audio or using Airplay for video).