Eleonora Gonzaga the Elder (not to be confused with her great-niece who was also empress) was a much sought bride by the Habsburgs, since Felipe III considered remarrying to her after his first wife died, and then she finally did marry Holy Roman Emperor Ferdinand II in 1622. However, despite their fifteen year marriage, there were never any childrrn produced. Maybe Ferdinanf II was too busy with the first phase of the 30YW to make babies (although IDK how involved he actually was with the war. I know his son, brother and brother-in-law actually fought, but I don't think I've ever read Ferdinand was the soldiering type)?
Either way, the childlessness strikes me as odd. Eleonora was old-ish for the time (23yo when married) although herstepdaughter-in-law was 25 and still managed 6 kids; plus all the other Habsburg-Gonzaga matches (where there was enough time, so Francesco III and Katherina of Austria's doesn't count) had produced issue. Not to mention that Eleonora came from a fairly fertile family where only she and a brother who married a twenty-years-older widow left no descent.
I also don't recall that Ferdinand II was so attached to his first wife that he sought a mother for his children rather than a wife for his bed.
PS: with the spate of Habsburg WIs of late, I thought I'd throw mine out and see what I get.