Note added December 14th: After the latest MacOS update (10.13.2), everything now works like before. The problem was therefore definitely with the initial High Sierra versions. Thanks again for a great tool!
I've had some of those issues ever since I upgraded to High Sierra. Contacted this forum on November 16th and was told to Clear Application Cache and rebuild macOSMetadata (checking Delete /.Spotlight-V100), but unfortunately it still did not work as before. I frequently use directory "2017" and all of a sudden Alfred would not find it (but that was the first one at the top of the list before). I just tried the latest (beta) version of Alfred, and now Open File does not seem to be available at all. I've been using the shortcut as before (Alt-Space, then Space). I've rebuilt again the macOS Metadata, but to no avail. I do see that spotlight finds the "2017" directory, but unfortunately that doesn't seem to affect Alfred. Included are a screenshot of Spotlight (with a search on "2017"), as well as a screenshot of Alfred (same search, on "2017").
I suppose the problem lies somewhere in the spotlight database or its access, since the problem started with the OS update...
I really appreciate Alfred, it's been an incredible tool for me! Thanks a lot for that great piece of software!