01-28-2019 06:17 PM - edited 01-28-2019 06:19 PM
IS has nothing to do with focus. It simply moves the image around on the sensor to compensate for lens movement, as determined by internal aceleration sensors.
CA is a problem anytime you have a non-flat piece of glass. It is the same reason prisms can split light into a spectrum.
01-28-2019 06:21 PM
"The lack of sharp focus makes me think the IS isn't working."
That is really is no indication. IS doesn't make a lens any sharper. It makes you sharper. I believe your only recourse is to have someone, Canon, check it out as you will always think something is wrong even if it isn't.