Canon EOS M200 Advanced User's Manual page 178

AF Method
The camera will keep moving the active AF point [S] to track subjects for Zone
z
AF when Servo AF operation is used, but under some shooting conditions (such
as when subjects are small), it may not be possible to track the subject.
Focusing with an AF-assist beam may be difficult with AF points near the edge
z
of the screen. In this case, move to an AF point in the center of the screen.
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