@BumblingJuicebox I have found this happening in my game since installing DU. And I think I've figured out what causes it most of the time. But if you use the resetsim cheat as @donald556655 suggests, that will clear it just about every time as far as I can tell.
What seems to cause it, especially if you have roommates like in a dorm or have a roommate on a residential lot, is the NPC roommates. Most times, when a sim wants to talk to your active sim, you'll see their face show up in the queue so you can tell why your sim just stops and stands there until the other sim gets there and says whatever. I seems to always happen that way if the other sim is a member of the same household but sometimes if the other sim is an NPC, it may or it may not.
But for some reason, the DU roommates don't show up in the queue when they want to talk to your sim. It also happens with other NPCs now too, but not as much. Sometimes they show in the queue, sometimes they don't as far as I can tell. And depending on how far away that sim is from your sim when the action initiates, it can take awhile before they get to where your sim is and say whatever it is they want to say. And until they do, the active sim just stops dead in it's tracks waiting. Once the NPC does say whatever it is, your active sim then can go about their business as usual.
And I've noticed that if your sim is doing something that the game won't normally interrupt like taking a shower, then the NPC will just stand there until your sim is finished and then say whatever it was he wanted to say. If your sim is doing something where the game allows conversations to happen during the activity, like doing homework, playing chess, or eating, the NPC will come up to your sim and start the conversation that can last awhile and make your sim take longer to finish whatever they were doing. So in that last case, you really don't notice what is happening, but your sim does stop what they are doing waiting on the NPC sim to say whatever it is to your sim.
For some reason though, it appears that the NPC roommates want to talk to my sims a lot, especially in a dorm so once I figured out what was going on, when one of my sims just stops like that, I routinely look around to see what NPC is headed towards my sim and if they are fairly close, I let them do their thing. If they are far away, I either reset my sim or the NPC. Resetting either one will break the action and your sim will then proceed with their day.
