In the event that cleanup needs to restore a piston, any piston that was placed after its power source was placed, based on the cleanup order, will remain headless. Then it will attempt to place the piston head as a block even though that doesn't exist, and ultimately cannot fix it.
Some other blocks such as fire and nether portals are also affected by this, and it will continue to attempt to place something it doesn't even have an item for
In the event that cleanup needs to restore a piston, any piston that was placed after its power source was placed, based on the cleanup order, will remain headless. Then it will attempt to place the piston head as a block even though that doesn't exist, and ultimately cannot fix it.
Some other blocks such as fire and nether portals are also affected by this, and it will continue to attempt to place something it doesn't even have an item for