If you try it a few times, it’s not always down and not always by the same amount. I described it as random, but few things are truly random in apps, so there must be a method to the madness.
Can confirm it does not behave this way on Android.
When tapping on the ‘+’ for an offer which has not yet been claimed, the unclaimed item(s) below it smoothly move up & overwrite the claimed offer, which then shows in the ‘Ready to use / Activated offers’ section.