You mention that the app hangs when you move back from the 2nd screen to the first. How have you configured the Back button to move back in the flow? Are you using OOTB screenflow and OOTB back functionality to navigate back/forward in the flow? Does the hang occur right after your load 1st screen again or does it happen when you invoke some action on the multiselect control e.g. focus into it? Have your watched the console for any errors when you navigate between screens and come back to the screen 1. Also have you queried the client cache to see if the values from the DP associated with the multiselect are still present or have they been flushed out? Are you OFFLINE during this entire interaction?
After raising SR we came to know that it is the 'Pega Express App' (downloaded from play store) issue. The app has limited functionality support and it was recommended to build our own custom app for iOS and Andriod.