A week ago I sent an app for review with 2 platforms (iOS + tvOS). It had a couple IAPs and I attached them to the iOS submission. Then I sent tvOS for review.
For my surprise, platforms are reviewed individually and with different timings. Perhaps tvOS / macOS has less released apps than iOS and their queues are smaller.
What happened, you guessed it, tvOS got approved and iOS was still queued. Consequence: people on tvOS couldn't buy any of the IAP because they were attached to the iOS submission.
Lesson learned: when having more than one platform in review, make sure you change app launch from automatic to manual so you can wait for both being approved and then release them whenever you want.