If the world spawn is set in an unloaded chunk, it will not register as a loaded chunk until a player has loaded it first.
This also happens when the world spawn is moved out of that chunk, it will not update until the chunk is loaded by a player then unloaded.

The test I performed was to have a repeating command block in an unloaded chunk, then setting the worldspawn at that point.
when the world spawn is set there, no messages appear from the command block until I teleport to that location. And when moving the world spawn to a different location, the messages don't stop until I move into and out of the chunk.