I'm having the same experience. Sandbox seems to be having an issue. I'm not sure what the root cause is. The information that the API populates in the SKProduct object is correct, but when the payment screen appears, the price is wrong. This is keeping the application from being approved during the App Review process.

Hi App Store Commerce Engineer, Please find the ticket I raised as well for my application. FB11827177. No response yet to the ticket. See my comments in this thread for what my experience is. Thank you!

Has this been resolved. I'm facing an issue where my app is rejected because the price in the sandbox is not displayed correctly. I've raised this ticket: FB11827177. I hope you can help!