I just picked up a pi zero to complete the collection of a Pi2 and Pi3! But...
I wanted to use the usb ethernet adapter I have.
Started from a bare image install. Had to manually download the net-usb-4.9.22-piCore.tcz (V6 version mind you for the zero) and went through the laborious process of adding it to /tce/optional, and adding it to the onboot.lst file from another usb drive from another machine...
So far so good, usb-ethernet is now up and I was able to tce-load -wi TC.tcz.
But no gui joy after several reboots and looking at the filesystem. startx doesn't work. TC.tcz not found.
Guess what - REMOVING the usb stick I used to manually copy the files (/dev/sda) and rebooting automatically launched the gui.
I thought it might have been the power supply, but a 2.5a supply has had no problems with my passive hub, keyboard, mouse, and a usb stick needed to manually copy that file.
I don't know if this is true or not (since I'm not going to try and repeat it), but it seems that the addition of a /dev/sda upon first reboot of piCore after installing TC.tcz got it confused?