We are also seeing the issue in our StoreKit 2 implementation since updating to iOS 18.2. In our apps we have been able to narrow the issue down to when we present multiple UIWindows at the same time.
I'm guessing StoreKit is might be having issues determining which UIWindow should be used to present to StoreKit UI under those conditions.
We have reproduced the issues in a small sample project and filed a feedback to Apple with number: FB16117689