In my game, certain save files not all, I have the same problem. But it happens with the auto change too. My Sim while wearing pj's will finish breakfast, carpool is outside honking and she just stands there. Whether I cancel the action or not and reorder her to go to work, she takes her time changing. Other times in that same game she changes clothes totally fine. Thankfully job performance has only been affected.
So you all mean that whenever your Sims are meant to change clothes, they just stand there for quite some time before they do change?
If that's correct, then it's not anything buggy about it at all. When you've just opened your game, some things haven't loaded yet because they'll only start loading when you start using them (like patterns in Create-a-Style). So when you then change your Sim's outfit, the game first has to load the outfit, the mesh and its pattern(s) and then change the Sim into that outfit. It can take a while to load but if you've already loaded an outfit once, it won't take but a second to load it again. The thing with Sims standing in front of the shower and beds for some time before they change is the same, the game has to load the outfit (or in the case of the shower, the nude skin plus pixelation) first.
And I never have my Sims change into their work outfits before work. That's because my Sims mostly take a bath or shower before work, or sometimes go directly out of bed, so they automatically change into their work outfit when going out of the bed or shower/bath before the carpool arrives.
(By the way, long time since I last posted so nice to see you again!)