Reproduction:

Step 1: Set you render distance down for testing purposes

Step 2: Set up some item frames and mobs on the spawn chunks

Step 3: Take some distance from them till you can't see them +20 blocks
(in this step you are putting them on "lazy chunks")

Step 4: Come back to the spot and you will not see them

• If you still see then when you come back try again distancing a little more

• Remember to not go super far away and fully unload the entities

This same issue has once occurred with chests in 1.8's final snapshots.