Hello,
I have a map series layout set up in ArcGIS Pro 2.9.2. My page is set up to use a standard letter size paper 8.5 x 11. I set a guide in my layout to have about a 1/2 inch margin from all four sides. When I export my layout to PDF, the top margin disappears and the text aligns to the very top of the page.
I attempted to lower the margin to 1 inch but the same thing happens. I also attempted to add a new line return in my text box but that did not make a difference either. What could be causing the top margin to disappear during export?

Layout properties showing page size.

Guides in layout view showing top margin.

PDF Export - top margin removed