The “<$levelN_title>” works fine if I put it in my main document or as a prefix on a section layout, (I’ve tested multiple numbers.)
When I put it in the header or footer, instead of processing to show that level title, I’m getting “<$levelNtitle>”. Ergo, my interpretation of the bug.
I’ve tried the various auto-search and replace settings (both in compile defaults and on compile), and those don’t touch it.
To replicate this error:
Select something with multiple levels for Compile.
Select a PDF format.
Go into Edit Format… > Page Settings > Header and Footer Text.
Use the “<$levelN_title>” in the header and/or footer area.
Compile.
You should then see “<$levelNtitle>” in the header and/or footer.
According to the complete placeholder list under the Help menu:
$levelN_title is listed under Document Variables, and so is not available in the headers and footers. I’d like to use the Document Variables in headers myself, which is how I found out.