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When you say it's not on their Timeline, are you looking at the Activity Log of Facebook to confirm, or just their profile feed? The Facebook Activity Log is where it should always display. The Feed is where it *can* display based on a lot of different criteria. The Activity Log on Facebook can be reached by clicking the link for it in the bottom right of the Cover Photo area.

Another thing to try is to set the news.reads action to allow multiple posts. Then, when the action is triggered again, the blue box will show a message like "Error: Action is already on Timeline". If that's the case, you know that even Facebook has detected the first post and isn't allowing a second. Then, you just need to verify it's actually there.

Let me know if that helps narrow things down or not.

Thanks,
Alex