Editor of manuscript assigned after reviews were completed
Each journal has its specific take, but the most likely explanation is that the peer review process took longer than usual and the same editor had expired and had to be reassigned, or that he was no longer interested in handling your manuscript and it was thus assigned to another editor.

In most busy journals several associate editors cooperate with the editor-in-chief, and it is likely that your manuscript was switched from one associate editor to another one.