Update
TL;DR: skip to accepted answer below: https://stackoverflow.com/a/44804086/474034
As mentioned in the comments by multiple people, this solution is not correct. The Thymeleaf documentation (see http://thymeleaf.org/doc/tutorials/3.0/usingthymeleaf.html), have in all their examples a version with www. included:
<html xmlns:th="http://www.thymeleaf.org">
See also the Standard-Dialect.xml on Github, which declares namespace-uri as:
namespace-uri="http://www.thymeleaf.org"
Original Answer
I had two different portions of code: the first was showing the error and the second was not doing it.
I observed that there is a difference in the xmlns:th attribute.
First Page: Not working!
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:th="http://www.thymeleaf.org">
Second Page: Working!
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:th="http://thymeleaf.org">
I removed the www. and it works for me!