I had an opposite issue: the chest was shining, I put the relic in my inventory, I was about to leave the tomb.. But my adventure journal was telling me that I still needed to "find the relic of eternity". Whaaattt??! It's in my sim's unrealistically sized pockets! I cancelled the quest and am hoping it will come back to me, since it took me the better portion on 1 1/2 - 2 hrs to fully get through the great pyramid.