If a subject goes outside of the AF zones of the camera, the camera can lose track of it if you do not correct your tracking. I do not think it really matters what camera you're using. Although, I have not considered either the M5 or the 5Dsr to be the camera body of choice for tracking moving subjects, or sports photography.
I think both cameras have a definite niche, in which they fit. I think the 5Dsr is best for stills with the best available lenses. It does not have the wide ISO range of 5D Mark 3/4, but it does have the very high resolution sensor and a sophisticated AF system. I'm not certain if most super telephoto lenses used for sports are capable of getting the most from the high resolution sensor in the 5Dsr. But, the lower resolution, wider ISO range, and higher continuous shooting frame rate of the 5D4 can probably do a better job at sports photography, especially under widely varying light conditions.
I have an M3, and I have found two good uses for it. One, the M3 is a great walk around compact camera, especially when I pair it with an ultra wide angle [14mm] manual focus lens. Two, my son is an executive chef and has discovered that the combination of 24MP and a DIGIC 6 make it great for macro shots of plates of food. The focus peaking display makes it easy to set up a series of shots that can be stacked, for an expanded DOF.
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