Here is the solution: if you have Avira installed in your Mac, uninstall it and see if the problem got fixed. If not, then the problem can be fixed through clean re-install the Mac OS latest version. And don't install Avira for Mac until it fixes the bug. (Avira is working fine with 10.13.1, but not 10.13.2)
I had the same problem after I upgrade by system from 10.13.1 to 10.13.2, and I tried all the methods recommended by other people, but those solutions just won't work for me. So I did a clean re-install my system, and the problem was fixed until I install the latest Avira to my Mac... There must be some kind of bugs that Avira has on 10.13.2. Once I uninstall the Avira, the problem just goes away.
To find this problem it took me 2 days, and I clean re-install the Mac OS 3 times to check at when and how the problem showed up....Hope my method will fix your problem as well.