Please send us the crash dumps for investigation.
Crashes in the dopus_thumbnails thread will usually be caused by something outside of Opus (e.g. if thumbnailing video files, the video codecs/splitters on the system become involved, and some of them have bugs that mean they crash on certain files).
The crash dumps will usually mean we can point to a particular component without you having to narrow it down (depending on the type of crash), and they'll also confirm whether the problem is in Opus or outside of it.