I made this very simple SVG in Inkscape 1.2.2: https://svgshare.com/s/rbx
The pdf export (default export settings) looks like this:
All of the horizontal segments are missing (everything else is there). The LaTeX typesetting is done with TeXText (although that shows up fine).
I've tried ungrouping, applying transforms, deep ungroup etc. (as inspired by other posts), and nothing seems to work. What's going on?