When the Nazis rose to power, they began a campaign of burning books deemed incompatible with the Nazi ideology. During these book burnings, were there any works that were completely lost? By "completely lost", I mean "Every single copy of that work was destroyed".
Magnus Hirschfeld, a researcher on sexuality and early advocates for gay rights amassed a huge body of research on homosexuality and transsexuality. In '33, he was heading and institute at the Charité University in Berlin. The Archive of his Institute was burned completely, a huge body of research was lost. This did not happen "just" because he was jewish, but because of the content of his Institute's research that was seen as demoralizing ("Entsittlichung").
Especially trans rights advocates in germany often quip "Everyone says transsexuality is new phenomenon. We where always here, the Nazis just burned the evidence"
Hirschfeld himself was travelling abroad and decided to remain in Switzerland when he heard of the book burnings. He died 1935 in Nice, France.
ETA This article on a magazine published by the Institute, Das dritte Geschlecht / The third Sex, provides some context.