Imperial Conditional Offer Confusion. What should I do?

I have graduated college a few years ago and received a conditional MSc offer recently. The school asked to verify a much higher college gpa as a condition for my offer. There is no way I can work on my gpa given that I'm already out of college, and I have submitted my transcript during application process so they would have seen the overall gpa.

Has anyone encountered a situation like this? Does that mean they could potentially rescind the offer?

Any insights/help is appreciated. Thanks!