Attacking Iron Golem bug

Ok I was spawning Iron Golems to fight some silverfish I had already spawned. The iron golems started attacking the silverfish as normal. Then I noticed one Iron Golem was attacking into thin air. It was frozen there looking down hitting every 5 seconds. Even if I moved it it would keep attacking air and not do anything. Eventually I killed to Golem but it was really weird when he was alive.