Hi there
Alfred v3.2.1[768] currently hangs on Sierra 10.12.2 (Macbook Pro 2016) when opening an App for the first time.
What is happening is Mac's "are you sure you want to open this app, you just downloaded it from the internet" () appears behind Alfred, with the window focus, freezing the Alfred window.
Steps to repeat:
1) Download an app like Bartender, Skitch etc from the web
2) Move the app to Application folder, give Alfred about 2 sec to index it
3) Try to open the new Application with Alfred (i.e. CMD-Space, type "Bartender", press Enter)
4) Alfred freezes
Upon killing Alfred with Activity Monitor, you'll see a screen like below appearing behind Alfred
Previously, on El Capitan, I think Alfred moved the modal screen in front of Alfred, and dismissed the Alfred bar itself.
Let me know if further info is required.