Testing this on a 16.9.0-SNAPSHOT local instance. At step 3, U1 does not have access rights on the page. Since it's not clearly defined, step 3 was meant to be done as U1. Nowadays, a default user doesn't have admin right on a space they created. For the sake of trying to match the test conditions, I added one extra step where the Admin needs to provide U1 with Admin rights on the NestedPage PageandChildren.
After this, changing the rights for U2 is not an issue. I think that somewhere along the way we agreed that Admin right would imply View right (which would fix this issue).
Closing this issue as `Cannot Reproduce`.
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