just like in https://bugs.mojang.com/browse/MC-65951 armorstands fell through the fence,
TNT entity fall through when being ignited above a fence.
MC-172108
Tnt being ignited above fences fall through the fence
Resolved
Duplicate
0
This is not a bug, its a feature. Since the entity is spawned inside of the blocks hitbox it will pass right thru it.