ViewModel's properties become null when navigating

I have two Pages, which share the same ViewModel. I did this in order to handle the same data when navigating from Page1 to Page2. The data that I need when I navigate to Page2 is the text of Page 1 entries, which are binded to the ViewModel. In the ViewModel I do PushAsync(new Page2()), but at this point all the binded text entries (from Page1) become null. What am I missing?