On my activity log on Facebook, I cannot get hidden posts back to my timeline and I cannot hide posts on my activity log. When I click, for example, Allowed on timeline and then refresh the page, it's still on hidden. Why?
Well its very weird behavior, The posts which you clicked to hide in your timeline they will be hidden untill you allow them again. As far as i know once you allow them again then you can see latest posts only. You can send your issue to facebook team, find this option in your profile and send your issue. https://www.facebook.com/help/contact/