Hanging signs placed with setblock don't have support bar (non-attached, of course)

/setblock 22 102 -10 oak_log
/setblock 23 102 -10 minecraft:oak_hanging_sign[attached=false,rotation=0]

 

The new hanging sign will not have a bar holding on to the chain, the chain will just hang in the air. It ought to have a bar above the chain that attaches to the adjacent block.