I’m experiencing the same problem: Many calendar entries are duplicated (some of them as often as 10 times). As I also see syncing issues from time to time, my problem might be solved by the commit you were referencing.
I’m using the current version from F-Droid.
Could you also send me a build with the respective changes? I managed to build an updated apk myself, but I cannot update the existing installation as I can’t sign it with the same certificate (and I don’t want to loose my settings).
Greets and thanks for the effort,