Item Frames Despawning at Random in Realms (Unknown if Single Player)

On my Realms server at spawn there are quite a few passive entities. I was making a few maps, and a few days later logging in the item frames holding them were mostly despawned. I am not sure if this affects singleplayer but it definitely affected the Realms.

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The attachment shows a map that has partially despawned. (It was 3x3).