Thanks for the tips! Using the LH site worked! I knew about the throne charges and even tried using the LH site last month but it didn't work for me. Just tried again with success. Turns out I was inadvertently selecting throne seats last time. They really should color code them or at least highlight the price! It didn't help that there was some sort of error on the page too.
Unfortunately, an error related to additional services has occurred. Please contact the Lufthansa Service Center. We apologize for any inconvenience. (15235 - 605)
Edit: Before I throw myself under the bus, I’m not so sure it was user error and not computer. I had taken a few screenshots that showed I selected 3A (which is a throne) but IIRC I also tried non throne seats in rows 2 and/or 4. I don’t have screenshots of those but I’m pretty sure I did play around with the site. I certainly remember being frustrated!