Raid Pillagers Spawn Underground

After activating a raid, wave 1 of pillagers spawned all underground. I had to follow the Iron Golem that was present in the village to get an estimate of where they could be. When the Iron Golem stopped and looked directly downwards, I knew that the pillagers would be directly underground stuck in a tunnel. I had to mine downwards, search for them and kill them. Other waves spawned just fine.