It would have the same root as Franz, Francis, Frances, Frank, et cetera, meaning either 'free man' or 'Frenchman.' That said, the only thing I could find quickly is a website saying that someone from the Philippines told the site Franzis is a male name there.. This is just an opinion, but if you don't live in Germany then it's probably not going to be a problem that it's considered a girls' name there.