XPath returning IndexError: list index out of range with Specific Example - xpath

Question

In order to test lxml's XPath, I have created a test file called output1. This test file is a small, isolated snippet of XML. Running XPath on output1 works as expected. However, when I try to run my code on the full test file that output1 is extracted from, the code throws an error that does not make sense.
This is the file:
<ADMIN-DATA>
<SOLAR>
<PLANET GID="SOLAR-SYSTEM">
<MOON GID="EDITABLE">
<EARTH GID="XPATH-EDITABLE">
<NUM GID="NAME">BongiornoPizza</NUM>
</EARTH>
</MOON>
</PLANET>
</SOLAR>
</ADMIN-DATA>
My script begins parsing PLANET's children (starting with MOON, who has GID="EDITABLE"). The issue is that I can't use XPath to get the direct and only child of MOON, which is EARTH. However, I can iterate using a for loop and manually get to EARTH. This is strange, considering I also tested it on an even smaller example using XPath and it worked.
The for loop for inner_node in node: works fine, and will get me EARTH.
Breaking code: (Using XPath to get EARTH)
if "function Comment" not in str(node.tag):
if node.attrib["GID"] == "EDITABLE": # passes
xpath_editable_node = node.xpath('./EARTH')[0] # BREAKS ON THIS LINE
name_node = xpath_editable_node.xpath('./NUM')[0]
print(name_node.text) # should contain BongiornoPizza
Working code: (Uses for loop to get EARTH)
if "function Comment" not in str(node.tag):
if node.attrib["GID"] == "EDITABLE": # passes
for inner_node in node:
print(inner_node)
if inner_node.attrib["GID"] == "XPATH-EDITABLE":
print("INSIDE")
name_node = inner_node.xpath('./NUM')[0]
print(name_node.text) # should contain BongiornoPizza
I can achieve what I want with for loops and manual iteration, but it would be nice to be able to consistently use the XPath library in a clean manner. I think I'm probably missing a simple thing and that's why it is not working.