Apologies for having missed this. As a true EOS M3 fan I shouldn’t have. Canon released EOS M3 firmware 1.0.1 back in July 2015. The firmware solves AF issues with the EF-S 55-250mm f/4-5.6 IS STM lens.
1. Improves the autofocus speed of an EF-S 55-250mm f/4-5.6 IS STM attached to the EOS M3 (to mount the EF-S 55-250mm f/4-5.6 IS STM to the EOS M3, the mount adapter EF-EOS M is required. The enhancement in the autofocus speed only applies when the lens is used with the EF-S 55-250mm f/4-5.6 IS STM)
Firmware Version 1.0.1 is for cameras with firmware Version 1.0.0. If the camera’s firmware is already Version 1.0.1, it is not necessary to update the firmware.
When updating the firmware of the camera, please review the instructions thoroughly before you download the firmware.
If the 6th digit in the serial number of your camera is either 0, 1, or 2, then it is equipped with firmware Version 1.0.0 e.g.
xxxxx0xxxxxx, xxxxx1xxxxxx, xxxxx2xxxxxx
Cameras with serial numbers other than those listed above are equipped with firmware Version 1.0.1 or later.