This seems to be recurring problem with the ixpand every time I plug it in to my iPhone 6 or iPad both iOS 11.4 it will not detect the ixpand version 5.0.3 and I have completed all the trouble shooting options time and time again. This was a present for me and I have backed up a lot of files on the ixpand 32g flash drive so very disappointing when it never seems to work. Sandisk definitely need to update and have a deep look at this recurring problem. For the price it cost it is not worth the hassles.
i have 11.4 and 5.0.3 and I am not seeing any detection issues. there may be an issue with the iXpand itself.
I would try connecting to a computer and see if the iXpand works there. If it does backup all the data and contact sandisk support as the lightning side of the iXpand may have an issue.