Chrome + XML: Input is not proper UTF-8, indicate encoding! What is the reason?

Question

PHP

Hello!
Tell me what could be the problem. There is an XML document that I form line by line in a PHP script (without XML lib). There is a product description block that must be included in CDATA with all tags that, according to the task, must be escaped. Everything seems to be clear, but in chrome an error is thrown out all the time,
Input is not proper UTF-8, indicate encoding !

while in mozilla everything is ok and complains only about the lack of xsl
And yet - the error appears despite the fact that the file is formed the same, in different lines, with each file update.
Here is the line itself and the symbol before which the error occurs (up to this point there is a pack of the same tags and everything is ok there):