Minecarts can switch rails when running parallel

I have 3 minecarts with chests running parallel a distance about 150² blocks (from a farm to storage).
Sometimes the minecarts with chests jump to a neighboring rail and block another minecart with rail. It seems to happen mostly when the chunks the rail system is unloaded, but it will not do it consistently.
I am running this on a Minecraft Realms server if that is any help.
Thanks.