Disappearing Heavy War Sleds

Hey All,

I'm currently going through a Realms of Chaos campaign as Ice Court Kislev

I currently have an army fighting Puppets of Chaos in the Trollheim Mountains, that among other things, consists of 2 Heavy War Sleds.

Twice now, it seems that my Heavy War Sleds have disappeared from my army with no cause. The second time was after I broke off a siege of the Forbidden Citadel after the Puppets of Chaos arrived with reinforcements. I believe the first time it happened after ending a turn with Maad's Map equipped. It had teleported me a short distance away, which is when I noticed the sleds missing.

I'm playing on normal. I'm relatively inexperienced with the game, so I wanted to ask whether there is a mechanic I am missing here. So far, it has only occurred with this one army.