The file-info thread may have gotten stuck on another file that it viewed. e.g. This sometimes happens if it tries to get information about a video file, and the combination of the file + the installed video codecs/splitters causes the request to take a long time or even get stuck in a loop and never return.
If it happens often, try disabling the Movie viewer plugin & restarting Opus as a quick test. If that seems to stop the problem, it's most likely being caused by a video file/splitter. (That isn't the only possible cause, but it's a reasonably common one compared to the other possibilities.)