The Lost Ark or the Hidden Ark?
When King Shlomo built the First Beis HaMikdash, he knew that it would not last forever. With that in mind, he had a maze of twisty tunnels built deep below the actual building.
Many years later, King Yoshiyahu saw that the Beis HaMikdash would be destroyed – as would indeed happen – so he commanded that the Aron (together with Aharon’s staff, the container of Mann, and the Shemen HaMishchah), should be be hidden deep down in those tunnels.
When the Second Beis HaMikdash was built, they left an empty place for those missing items. But they were never really missing. They were just being stored in a special safe spot, deep within the Temple Mount.
And they are still there today – so it’s not a “Lost Ark” – it’s a “Hidden Ark!”