I have checked with internal and external testers and my devices and simulators, everyone sees the in app purchases but I just had my submitted rejected for the second time with the comment that these in-app none-consumable purchases cannot be found with the submitted binary.
That's because you have prior knowledge as to where they are located, which doesn't guarantee that reviewers see them.
by navigating through only 3 buttons
How sure are you that those 3 buttons clearly appear under the latest OS version? Have you tested the app with an iPad? A toolbar button may appear as a 2 x 2 pixel dot under 26.0 unless you are careful with it. I would take a good look at the system details they give you.
along with detailed instruction
Perhaps, you are making the situation worse. I would make it concise so that they will not be overwhelmed