The bug
Upon replacing an area that had a campfire in it using a structure block, the campfire is removed like normal however the smoke stays behind. Reloading the world fixes this.
How to reproduce
Place a few campfires in the area; you are gonna load the structure.
Load the structure
"minecraft:village/savanna/houses/savanna_weaponsmith_2"
→ ❌ Smoke particles stay active
I should mention that after reloading the world it goes away; so it isn't really important