Yes, Gangloff is in Germany today, but it has also been French several times over the last few centuries. It lies in a part of Alsatian Germany that has been in dispute for hundreds of years.

I've run into the usual census-taking mis-spellings, but I've found that Gongloff (and in Europe, Gangluff) are variants that have stuck through the years. I'm inclined to believe it had more to do with illiteracy and phonetic spelling by family members than anything else.