Good luck with KIA, hopefully you will get it replaced under warranty like a couple of us have done already.
Where we have lived for the last 3 years our temps don't get down to sub zero's (celsius), probably 3 or 4 (37 fahrenheit) has been our lowest. We did have a couple of zeros /-2's for the couple of years before that, but I only notice the first signs of cracking about 18 months ago.
I'm wondering if it might not be a simple cold expansion/contraction issue. The crack is very near where the spoiler is bolted. What if somehow water has got into this area and it has frozen causing the plastic to be pushed away from the glass.
This would explain why it doesn't happen to every Sportage, there needs to be some source of water in the first place, somewhere/how for this water to be trapped and then the freezing overnight temperature. I'd guess that the two sided tape that holds the end part of the spolier is put on manually, so each spoiler is slightly different, maybe the tape could be placed in such a way to trap this elusive water ? Then there is how the car is parked over night, i.e. maybe on an angle that traps this suspect water. To have all these variables come together at the same time would be quite rare, I think this explains why there are very few vehicles with the cracks.
Well that's my conspiracy theory on cracking KIA spoliers
