While playing a Survival world in Realms, I noticed one of my two named Iron Golems missing and searched the area for fence breaches or cave-ins but found none. After switching to creative and remaining very close to the other Iron Golem, it too vanished, likely while I was very close to or inside the loaded chunk. The only similar issue I saw posted involved animals dying while chunks loaded and unloaded, but these golems didn't die... they just vanished, and right under my nose as I was within 20-100m both times.