When i want to sync two folders with many files and sub-folders DO crashes. The folder contains 67724 files in 5390 folders (BOOST, QT and other sources). After DO reads all folders it compare the files and then crash.
If you put Opus into Flat View mode starting at the same folder, do you also get a crash?
It may be one of the files in the folders triggering a crash when its information is extracted for the columns you have in your file display. For example, if you have the Description or Dimensions columns (or several others) and any video files in the listing, then Opus will rely on your installed video codecs to provide info on them, but sometimes they go haywire with certain files. (Sometimes it's also a bug in Opus itself or an Opus plugin.) This FAQ can help if that's the case.