Marino, Akerman, Mullaly
So are these three just not on the show anymore?
shareI think Åkerman is gone, at least for the time being. I think she's just busy doing other stuff, I wouldn't be surprised if she comes back when her schedule permits it.
As for the other actors this season not every actor will be in every episode. I'm not sure why, but I'd guess it's to cut costs (Smaller cast = less people to pay). I used to watch the NBC drama Parenthood, and in their final season they only had the full cast in the final episode, in the rest they rotated the actors and always had at least two characters "missing". It's a decent money-saver, with good writing you don't think about the missing characters.
Åkerman was working on Billions at the time this season was shot, and just had a small cameo. Mullally was involved in "You, Me and the Apocalypse", but she will be featured in half the episodes of the season. Ken Marino was missing from the first leg of the season, but is involved in all the other episodes. It has little to do with the order the episodes are shot, it was just a coincidence, or a creative choice.
You have to remember that the entire season must be shot in something like four or five weeks, and that the cast is paid very little, as it was mostly a labor of love with a small budget. The producers knew from the start when they were writing that Åkerman couldn't be involved and that Mullally would just have a short span during which she would be available. And Lake Bell must have been busy working on her own projects as a director or film actor in parallel. Actually, it's likely that the episodes are shot out of sequence, with different directors working on different episodes at the same time. That's why Cat can just have a cameo in one episode, as she has a bigger part in another, shot the same day.
But one striking thing is that a lot of the season so far has revolved over Erinn Hayes. Lola Spratt had to take over lines and scenes that would have been given to Valerie Flame or Cat Black in previous seasons, and she's been killing it.