I had 2 swarms come out of a hive on April 28th.
Then from the same hive I had a 3rd swarm on May 6th.

Can anyone explain this.

On April 28th the first one was a large normal swarm and the second one was smaller.
On May 6 the swarm was an average size swarm.

The remaining bees have eggs/brood/ etc. All the queen cells are empty.