Steps to reproduce
/give @s stonebrick 1 4
Expected result
You get stone bricks.
Observed result
You get smooth stone bricks. These look the same as stone bricks but they do not stack with stone bricks.
Smooth Stone Bricks are in the code and obtainable thru commands.
What command specifically are you using?
Are you getting this item in vanilla, or only with a behavior pack or template?