I haven't read the entire thread and don't know if it has been discussed but the OP might want to consider adding this to the list of problems that cause routing errors.
Avoid using the "Take Photo with Friend" interaction. I am sure everyone knows it was broken with a patch and that sims will just stand and stare at one another. But the problem is that it leaves an invisible rug behind that blocks those tiles the sims were standing on in the game. I think that if you use testingcheatsenabled and buydebug you may be able to see the invisible tile as a white block and you might be able to delete it with MOO but I have heard in some cases that people had to bulldoze a lot and replace it with a new copy to fix the lot. If, for example, in game play your sims can no longer open a refrigerator that was previously working because something is in the way there is a good chance there is an invisible rug with an incompleted interaction in front of it. And I have no clue how you would remedy this if the interaction occurs somewhere that is not on a lot that can be edited or replaced.
There may be other bugged interactions like this but the one I know about is "Take Photo with Friend." Also, I have never read about this elsewhere and it may cause these routing problems or not. I don't know. But if you have a sim that throws a Potent Cure Elixir at a vampire the vampire gets cured just fine but the vampire freezes as well as the sim that threw the elixir freezes waiting for the interaction to complete. If you reset the former vampire it allows the other sim to move on as well. But I have been wondering if maybe a rug gets left behind in that instance.
