Is it only when searching below your Dropbox folder, or happening for all folders? Is it only when the search, or results, contain certain file types? (It may involve a 3rd party component used to search inside a certain type, for example.)
Which version of Opus is it happening with? (The subject says 12, message says 11.19, profile says 9.)
If a crash dump is created for the crash, please send it to us and we may be able to see what is failing, and whether it's Opus itself or another component, which should help fix the problem one way or another.