The only thing that got the installer un-stuck for me was to click “Start all” in the Download Manager AFTER the installer got stuck. MAKE SURE YOU CLICK 'Start all' in the Download Manager, NOT just Start Download on whichever game you are trying to install/update. Only thing that worked for me was to go to the Download Manager after the installer stalled out, and then pause and restart all downloads (even though Overwatch was the only game I was installing). I tried launching as admin and reinstalling app to no avail. I had the same problem (on Windows 10), the installer kept getting stuck on 'Initializing 0% (528/528).
