My favorite horses keep disappearing!

My horses keep disappearing and Im not sure why! Today two of my horses just gone. This is not the first time this has happened, it has happed 3 times this month and today was the 4th. I’ve googled why this keeps happening, apparently it has to do with the horses being transported between non-chunk and chunk blocks. I have no clue in what that means. I have named and tamed my horses, they have a big pin and should other wise not be disappearing. I’m sure that other people have this issue. I would love if this can be fix so I can have horses without stress. Thank you.