Canon EOS M Basic Instruction Manual page 184

6 Shooting Night Portraits (Night Portrait) (With a Tripod)
Tell the subject to keep still even after the flash fires.
If you use a flash with the self-timer, the self-timer/AF-assist beam lamp
will light up briefly after the picture is taken.
When shooting night scenes or other scenes where multiple point-like
light sources appear on the screen, the camera may not be able to focus
automatically. In such cases, setting the [AF method] to [FlexiZone -
Single] is recommended. If the camera still cannot focus automatically,
set the focus mode to [MF] and focus manually.
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