What you were doing when the issue happened
I was trying to add videos to watchlist with DownVid workflow, and after selecting a file in Finder, I tried to use shortcut(cmd+opt+\) to file action, it does not work. (It does not work even after changing the shortcut for file action)
Whether you were able to replicate it a second time by performing the same action
I does not work consistently (even after rebooting)
Include any screenshots that might help us
Nothing happens (the shortcut does not work completely)
Include the Alfred version & build number you are using
I checked it with the latest version, and upgraded to pre-release version hoping the issue is resolved, but it is not resolved yet in the beta version.
(Currently using Alfred 3.6.2 pre-release)
Include your OS X version
macOS Mojave, Version 10.14 Beta (18A314k)