What I was doing prior to entities disappearing: Before armor stands with armor, and paintings, disappeared I had been based near 2091 73 -3605 using a portal that came out at Nether coordinates 342 60 -459. I was in the Nether for over an hour, and died several times to respawn at 2100 65 -3657. When I returned the regular way I ended up at an overworld portal near 2774 63 -3584. From there I teleported back to 120 64 -24, my base.
Single player/Nintendo switch
Despawns were near one of my base spawn points. I had changed spawn point from 2100 65 -3657. Paintings in a nearby village were not affected.
I had been experiencing despawning of pets and villagers (even those with name tags) persistently, but not more frequently.
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Same problem - I was exploring when I found eyeless llamas with beige textures and eyeless black horses. I reloaded game and THESE animals came back correctly; however, when I went back to base the Trader's llamas were also beige and FLICKERING. Nintendo Switch.