I have some XML in this format:

<ROOT><DOCUMENT>
<CHAPTER>Chapter One</CHAPTER>
<CONTENT>This is what happened in Chapter 1.</CONTENT>
<CHAPTER>Chapter Two</CHAPTER>
<CONTENT>This is what happened in Chapter 2.</CONTENT>
</DOCUMENT></ROOT>

I have a pre-tagged template where the <CHAPTER> tag maps to a paragraph style with Keep Options, start paragraph=Next page (i.e., every new chapter should start on a new page). The <CONTENT> tag maps to a basic paragraph style, and <ROOT> and <DOCUMENT> are not mapped.

Notice there is a line break in the XML after <DOCUMENT>.

After importing, the result is that page 1 appears blank (because of the line break) and Chapter One starts on page 2. If I go into the story editor and remove the line break so it looks like <DOCUMENT><CHAPTER>, it fixes the display so Chapter One starts on page 1.

To replicate, import the test XML into the test template, both found here:
https://drive.google.com/drive/folders/1xB39ObvHsGSQVviq1d-H0QkZ1Dk65sRQ?usp=sharing

I had asked in the forums if there was a solution for removing this line break automatically, either with XSLT or a script in InDesign (we are not able to change the original XML output),. I was told it might be a bug -- unexpected behavior with a return that is outside of the content that it should be placing.