my spotlight tool bar disappears after I type in 3 letters

I think it has everything to do with the Safari 12 update. Turn OFF (uncheck) the "Bookmarks & History" option in Spotlight pane in System Preferences. The problem will stop until Apple fixes Safari.

Here is the thread I started yesterday: Spotlight crashes after typing a few letters since Safari 12 update

How to test an issue in another user account on your Mac - Apple Support

It does not look like you're using Sierra. I am using Sierra. And all of the other new threads about this issue are being reported in the Sierra board. It's very possible the OP posted his thread in the High Sierra board by mistake, especially since his tagline says he's running iOS on a MacBook Pro.

See this thread in the Sierra board: Spotlight search always quits itself when typing.

- It seemed to work in Safe Mode. But then it also seemed to work after booting out of Safe Mode until it suddenly started crashing again.

- It does NOT work when logged into a new Admin account.

- It does NOT work after reindexing. (adding drive to Privacy and then removing drive)

- It does NOT work after reindexing via more forceful methods such as deleting the invisible Spotlight files on the root.

- It works during a reindex but starts crashing again after index is complete.

- It always works when "Bookmarks and History" is unchecked.

- It always worked before Safari version 12 update.

If you'd like to see part of my crash log, it's posted in my own thread about this issue.

Spotlight crashes after typing a few letters since Safari 12 update

Ok, well great for you... meanwhile, a bunch of people suddenly start reporting this problem within a day or two of the Safari 12 update. I counted about six new threads about Spotlight crashes in last two/three days, so something's up.

I run EtreCheck all the time and keep my system pretty clean. Not sure what I'm supposed to be looking for there since I'm not having speed or performance issues.

I would think the crash log would be incredibly more useful to anyone that can read it.

Thank you, thank you, thank you. This solves the problem.

Your take is also confirmed by Apple to be a conflict between Safari 12 and macOS Sierra.

I had conversations today with two Apple chatbots (Colleen and Maria). Chatbots are generally a waste of time (spending the first 10 minutes retyping your complaint and explaining how they empathize with you). But "Colleen" said once you upgrade to Safari 12, there is no going back; the only solution is to upgrade the OS.

However, you turned out to be smarter than the chatbot.

Unfortunately I can type more than three letters (and with "Bookmarks & History" checked) in Spotlight without it quitting even after the Safari 12 update. So I don't think that's it.

Okay. Doesn't seem to matter for me in Sierra either.

Try while in Safe Mode.

Use safe mode to isolate issues with your Mac - Apple Support

Other threads about this bug appeared this week:

Spotlight search always quits itself when typing.

Same here. It started with the update to Safari 12. The reply from the chatbot named MoonJ was terrifically unhelpful.

Assuming it's a Sierra issue it's unlikely to be fixed since High Sierra is out and Mojave will soon be. I can check my Sierra guest.

As I said, try it in Safe Mode. It's possible the users having a problem have something in common installed.

An EtreCheck report might be more useful.

http://www.etrecheck.com/

I see. Well perhaps fresh eyes might see something but it's your choice.