A new wrinkle...
So as I said I eliminated the "MXF media errors" by rolling back to a previous CC version. This did not, however, solve the problem that started this thread - choppy, hangy playback during editing. Yesterday I processed a show that was live-cut using a BlackMagicDesign ATEM Television Studio, and recorded to a BMD Hyperdeck Studio, encoded in BMD's house version of ProRes422.mov... My first go-round with this flavor of media. Of course I didn't find any sequence presets that seemed to match what I had, so I just pulled a clip to the timeline and let PrPro decide what to do with the sequence. It chose "AVC Intra class 100" - OK, whatever works. While editing (I didn't have a whole lot to do except trim it up, add titles, and mix down the audio) I watched the event viewer rack-up at least one audio dropout (with judder/freeze in the viewer) about every 90 seconds of operation for about 2 hours. When I finished up, the "match settings" export was a .MXF file (dun dun dun....). Not sure if this means that my dropout/freeze problem is not associated with .MXF source files (since the source was PRoRes422) OR if perhaps the "AVC Intra 100" sequence is related to .MXF somehow and is thus a common denominator between this sequence and other sequences that used the Canon XF sequence preset.
Sorry to muddy the waters with this new info - I'd be happy to answer any specific questions that occur to you or try some other tests that seem appropriate.
Eric