My guess would be a combination of things. I believe, generally, that Princess moves Captains among the vessels at certain intervals to keep them fresh in a way, but also keep them current on the different vessel classes, etc. Also, the introduction of Sun meant new assignments and shifting and a need for two new captains to fill voids left by moves to the Sun. I recall a posting about one of the captain's needing time off for some personal situation, so that triggers a shift and then again when he returned. I imagine things will settle down again into the regular 2-captain rotation, but you should expect some movement around the fleet at times as had been the case over the recent years I have been paying some attention.