If the Vertical slabs version of this campfire is placed it crashes the server until the block is edited back out.
Also if you place a campfire on top of another campfire you have the same results.

idk what you mean by the "Vertical slabs version of this campfire" but that sounds like something to take up with them, not us.

This sounds like your issue: CJMinecraft01/DoubleSlabs#182
DoubleSlabs has had a lot of issues with campfires recently, but it just updated so give the newest version a shot :)