EXO 'Dance'

[vorpal+5 (OP)]

My only EXO post in my playthrough is constantly being replaced, position lasts between 5 days and 60 (when things are calm!).

[nuclearslurpee]

This is not a bug, this is how automated assignments work. The command module jobs like XO are usually considered to be lower-priority than ship commands, so when a new ship command opens up (from construction, deaths, etc.) it is likely that an officer assigned to a subcommand job like XO will be reassigned to a ship command role.

One common cause here is if you are building a large number of fighters which do NOT have the "No Officers" checkbox ticked in the class design window. Fighters tend to be built frequently and take your low-ranking officers out of subcommand positions so they can command the fighter - I usually don't let officers command fighters because of this (and because having a LCDR in charge of, like, three guys seems a little silly to me).

[vorpal+5 (OP)]

Yes, that would explain indeed, I'm producing fighters (or more like Shuttles/Pinnaces) and they have an officer (the Melisande Pinnace is a 500-ton craft with 2 sensors and 17 crews).

If I name one manually, will he stick, as some officers do when you name them by hand?

[nuclearslurpee]

If I name one manually, will he stick, as some officers do when you name them by hand?

No, you need to turn off auto-assignments or disable officer assignment to the fighter class(es). That said, it's not worth worrying about unless you find yourself lacking for XOs generally because your fighter wings ate all the officers.

[vorpal+5 (OP)]

Sorry to be a pain on a fairly minor point but ...

1. Disabling auto-assignment is a general, extreme measure. I'm fine with auto-assignments in general for all my ships; it's a lot of micro-management otherwise, and I do appreciate the 'non-optimal distribution' that results from the routine. 
2. No assignment specifically for fighters. I did not know it was an option, but does it mean you chalk off the Fighter Combat skill for all games and intent? Seems extreme too.

[nuclearslurpee]

2. No assignment specifically for fighters. I did not know it was an option, but does it mean you chalk off the Fighter Combat skill for all games and intent? Seems extreme too.

As far as I know, there was never implemented any case in the auto-assignment code for fighter-specific skills. It is a rather significant omission, probably worth a suggestions thread post.