Seems like executive officers aren't assigned, at least for me in my games. Dunno what the requirement is for that but it seems strange I have none at all.
Maybe this is more suggestion-y but it would be great if there was an option also for auto-assign to fill empty spots on ships after everything else is done even if they don't have an applicable bonus. In priority of promotion grade or something.
EDIT: Apparently my ships don't have COs also, I don't have enough officers it seems. Others have reported XO assignment working. However, it seems like commander priority isn't working properly. I set my larger ships to have a higher commander priority but all the commanders are still hogged by the smaller ships with a lower priority.
All types of officers are assigned automatically in my current game, including XOs.
Commander priority for ships isn't working, however, I can confirm that.
I have commercial ships with 0 Command Priority, DDs with priority 2, and CAs with priority 5. DDs and civilians were filled first, while CAs are not getting officers. There were not enough officers of required rank (Captain) to fill all the ships before the assignments took place, so priority should've picked the CAs first, then DDs and only then civilian ships. But CAs were not given priority.