I don’t have any solution to your problem but I wanted to share that I was facing similar auth related issues with a LiveView app. In my case, the iOS version was very old and I think there was probably some feature that iOS didn’t support (that is required by LV). As soon as I upgraded the iOS version, the issue automatically resolved. To this day I have no clue what was the root-cause.
Maybe ask the client to update the iOS version if they are on a pretty old version. I know it is an unrealistic ask in certain circumstances but maybe it is a viable solution for you?
