I copied all my data to an external hard drive and used that as my main hard drive for a few days. After that I noticed a slight delay when bringing up spotlight, so that when I search for "Safari", it searches for "fari" instead, as I am used to being able to start typing close to instantly.
I just associated that with the fact that booting from an external drive is slower, however, even now when I have copied the data back to my internal drive and boot from that, the delay persists. I have reindexed my drive twice.
The problem also exists on the Guest user and my other user, so the problem does not have anything to do with my user/home folder. I am on macOS Mojave 10.14.3.
EDIT: Even after updating to 10.14.4, the problem still exists.
EDIT: Also on 10.14.6
Best Answer
Note: I can't take credit for these solutions, however a few of them have worked for me in the past.
Solution #1: Kill SystemUIServer
Launch ‘Activity Monitor’ (located in /Applications/Utilities/) Locate the process ‘SystemUIServer’, highlight it, and click the red button “Quit Process” Within a few seconds the menubar will rebuild itself and often Spotlight will magically work
Solution #2: Rebuild the Spotlight Index manually
Launch ‘Terminal’ (located in /Applications/Utilities/) At the command prompt, type this exactly: sudo mdutil -E / You will be asked for your password, provide it, as this command requires administrator privelages to run You will receive a confirmation message saying that index will be rebuilt Wait until index is finished rebuilding, this can take a while depending on the size of your hard drive, amount of files, etc. Note: You can also rebuild the Spotlight index with MainMenu, mentioned in Solution #4
Solution #3: Change Desktop Resolution
This is a strange fix but it works everytime for me when my Spotlight menu icon highlights but the search form doesn’t appear Open “System Preferences” via the Apple Menu Click ‘Displays’ and select a resolution smaller than what you are currently using, 640×480 seems to always work Select your native resolution again, changing your screen resolution back to normal The Spotlight search tray will magically become available again
Solution #4: Clear caches and preferences
Clear caches and preferences relating to Spotlight, this is best done through either the free tool OnyX, or the free tool MainMenu, I recommend MainMenu because it’s easier for novices
Note: Some users discover that just cleaning the Font caches is adequate to repair a screwy Spotlight, but it won’t hurt to clear them all
Solution #5: Reboot your Mac
This should almost be listed as #1 just because sometimes a simple reboot will fix Spotlight, but if I can avoid a reboot I will, and often, a reboot isn’t good enough What do MDS and MDWorker have to do with Spotlight? The MDS process and mdworker processes usually run concurrently on your Mac when Spotlight is indexing your Mac. Let the processes finish running to complete a relevant search index of your Mac filesystem.