@isabelleangelinaWhen I bring 20 - 30 sims to one spot, this happens from time to time. I find it's more related to your P.C hardware. The older the comp, the harder it is for Sims to run. When I notice it happening, I just pause the game or go into build mode for a bit. It allows the program to catch up.
For a better understanding, we will take 3 sims and call them Bob, Vern and Julie. Lets say you tell Julie to talk to Bob. Bob is on the swing set with Vern. Unless you cancel the swinging, Julie will just continue to stare into space and wait until Bob and Vern are done their command.
Now let's add more sims. Jim and Peter. Jim already has a command to talk to Bob and is waiting his turn to complete his command pushing Julies command back even further. Peter also has a command to talk to Bob.
So until all those commands get pushed through .... Julie is just going to stand around doing nothing. Sometimes the game will cancel Julies command because Bob is just too busy.
Add more Sims to the equation all trying to do something and the system just gets bugged out. Eventually, the game throws everyone into debug. you can see when the PC / game just give up because all the sims on the lot will go into (I can't think of the technical name for the pose right now so I will just call it standing starfish) A full debug command goes through and everything gets refreshed cancelling all commands.
You can manually debug a sim by shift clicking them or you need to shift click debug the object your trying to interact with. It should reset and get your sims on their way. Or, wait until your P.C catches up. But again, timing will be very much influenced by your P.C hardware.
One mod I will recommend, is the forum approved MCC. Go into settings and cut the population in zone down to a number that will ease up resources on your comp. I think default is 20. Try 10 and see if that helps. Also, custom CC with high pixel counts will hurt P.C performance as well.
Last, if you were running a heavily modded game prior, you may want to keep those mods out and do a repair on your game files. I was using some sort of life mod... I can't remember the name, but when I removed the mod, it seem to have left a bunch of holes in my sims coding. When I tried to play, those sims were bugging out badly and prompting errors. I ended up having to do a repair on the game. Started a fresh instance of sims 4 and restored those sims via dropping them from my library. After that, they stopped bugging out.
