Any idea what might be making my Touch Bar and Touch ID NOT work only in Safe Mode?
Assuming I understand your problem correctly (i.e. this issue is not present during Safe Mode) then your best bet is to investigate login items, fonts, and kernel extensions. 

Investigating login items, fonts, and kernel extensions

Let's start with Login Items:


Startup normally
Go to System Preferences > Users &amp; Groups
Select the Login Items tab
Take a note of your Login Items 
Now remove all of them by highlighting them and clicking on the - button below
Restart your computer


Now your Mac will boot up without those login items loading. Test to see if your Touch Bar and Touch ID work okay now.


If they work okay, you know one (or more) of the Login items were causing the problem. You can then add them back in one by one until you've identified the culprit. Problem solved.
If they still don't work, it's either a problem with fonts you've installed yourself or with a 3rd party kernel extension. A little more info below:


Fonts:- You can remove any of the fonts you've installed yourself to see if this makes a difference.

Kernel Extensions:- You can open Terminal (found within your Utilites folder) and enter the following command:

kextstat | grep -v com.apple

The above command will list 3rd party kernel extensions (you may need to stretch the Terminal window so it's easier to read). Look for anything you don't remember installing, or something that belongs to software you've removed, or just anything that looks out of place. Remember though, this is a list of 3rd party kernel extensions and therefore any of them could be causing the problem.

Create another user

If your Touch Bar and Touch ID still don't work after going through the above process, you could create a new user in Apple > System Preferences > Users &amp; Groups and then log into that user to see if the problem persists. If it doesn't persist, it may be better to use that user (or create another one you're happy to use) and migrate your data across to that account.

If all else fails

If none of the above works it may be time do a totally fresh installation of macOS (your question didn't specify whether you had already tried a "fresh" installation - but if you've already tried this then it may be best to try installing an earlier version of High Sierra).

NOTE: Make sure you have a current backup if you decide to do a full fresh installation of macOS.