Hm, we did not change this in openLCA 1.7 compared to previous versions. To restore the navigation, just go to Window/Show views/Other, and then again into the folder other, and there is the navigation view. OpenLCA tries to save the last state with which windows, "views" were open, and restore this. Maybe you minimised the window, then it is only a small icon, see my screenshot below.
Hth,
Andreas