Placing a trial spawner in Creative, adding a mob via spawn egg then switching to Survival to activate it breaks the spawner. It completes one trial (spawning 6 mobs and ejecting loot), then it loses the spawn data, but still goes into cooldown. When the cooldown completes, it's state either becomes "inactive" (the same as before placing a spawn egg in it) or starts switching between "inactive" and "waiting_for_players" really fast. Using the /data get command shows it lost the spawn_data it was assigned. The spinning mob also disappears from the center.