Or accessing a null collection. This also happens when fighting transforming (or traitsummoning, like Daemonic Pact, which works the same way) troops that aren’t connected to a specific player. They always summon at level 1 with no trait - you’ll see this happen sometimes with Daemonic pact fires in Dungeons and explore.
For non-player teams, they used to access the enemy’s starting troops as a “collection” and would traitsummon at the correct level if one of those troops was in the battle when it started (Infernal King for example would always come back at the correct level if he was part of the initial team). However, this also led to a bug where the stats of that troop after it had been difficulty boosted were counted as the base stats for any future summons of that troop, leading to situations where an Infernal King could revive at 9x base stats if you played on Warlord IV, or the Giant Spider in The Reaver challenge summoning a 9x stats Spider Swarm, or the Dark Master in Thralls to the Wall summoning a 9x Thrall, etc, but any troop not in the battle when it started was polled at base stats (times the difficulty multiplier). I assume the “fix” got us to where we are now, since this no longer seems to be possible.