If a Living Monument is chosen as the target building, and the creature-end of the chain gets removed later, Draknor's Chain will start to treat the monument as a creature-end of the chain, rather than the building-end, which it was originally chosen as.

I had a monumented Blunderbuss Squad, that I cast a chain on to get rid of some creatures by pulling them next to the squad and shooting them. After the first one died, I could no longer choose a new creature for the chain, and could only choose buildings as the other end of the chain.

Suggested fix: making both creatures and buildings valid targets for a Draknor's Chain that is enchanting a single figure which is both a creature and a building.