The bug

Using the minecraft:summoned_entity trigger in an advancement doesn't account for a bunch of entities a player can create directly via placing of an item:

1. minecraft:armor_stand
2. minecraft:painting
3. minecraft:minecart
4. minecraft:boat
5. minecraft:lead
6. minecraft:fireworks/minecraft:fireworks_rocket

(also, it won't work for spawn_eggs, but this might be different issue).

How to reproduce

1. Download the attached data pack datapack_MC-117900.zip and place it in the datapacks directory of your world folder
2. Open the world
3. Place an armor stand
   → The advancement is not made
4. Place two snow blocks and a pumpkin on top of each other to spawn a snow golem
   → The advancement is made