Been noticing that whenever I move mxf media around to keep it organized v8.6.4 gives a beachball during the scanning process rather than a progress bar and feedback. Appears the app has crashed but if you wait for a really long time it eventually finishes and saves. The save displays a progress window and feedback.
Mac Pro, mid 2012, v8.6.4, os 10.11.6, 64g ram, internal hd.