@Laci_K Not sure if this will help you. But back when I used to make a lot of Mac apps I always found it helpful when the customer would send the crashlogs and I symbolicate those to see exactly where the crash is (assuming it was not a garbage reference count issue):
Those are usually located here:
*~/Library/Logs/DiagnosticReports/
I think I recall seeing your app uploading stuff like this via ?Crash-alytics? but sometimes the actual log is easier:
Here is some info for those who may not be super comfortable with getting to those folders: