The emerald ore generation does not offset by 8 X and 8 Z, so it will sometimes generate on a chunk boundary and load a new chunk during ore generation.
net.minecraft.world.biome.BiomeHills.EmeraldGenerator#generate (MCP names)

Other ores offset their generation by +8, +8 in order to generate properly. See net.minecraft.world.gen.feature.WorldGenMinable#generate (MCP names).

I made a reddit post to help mod makers follow this rule, and while looking into it I found that vanilla emerald ore has this issue.