I hydroplaned my 2013 AWD 2.0T ATS and smashed the front end into the concrete barricade. I ended up with a entire front clip replacement. including the drivers side suspension. (I used a donor car I bought, and why I still have other ongoing repairs)... Long story short, on my vehicle, the rack and pinion stripped a tooth off one of the gears, I had a "dead spot" in the steering for awhile until I got it replaced. It would "line up" if I drove it in reverse with the wheel turned, and then resume off-alignment after a short period of driving and steering. If this sounds similar I would consider replacing the rack & pinion.
Its not a cheap, or easy fix, I had it quoted at a few different shops to get it done, (Labor only -> $1,100 - $1,700 here in Houston TX)
I have an extra one, new in box. I ended up shipped two parts from the supplier on their own fault, they told me to keep it. Let me know if you want it. It's a Detroit Axle re-manufactured part, never opened. I can part for probably $700-$800 or so, I'll check the current price on it. I'm not 100% sure if this part will match exactly, probably.. you'll need to check. I think the 2013 and 2015 had the same rack.