I am currently experiencing this issue, with the main sim on my household, but no other sims, and specifically when she comes back from work. It's on the Seabreeze Scenic lot in Gibbi. She will walk halfway onto the porch towards the only door, in or out, of the house and it will pop up with a padlock above her head. I have tried every solution that has been suggested, from flipping the door, buying/selling the door, moving her out of the household and back in, repairs, reloads, you name it and nothing works. She never has the neighbor tag above her head, and any and all mods I've used previously have been removed. While I was trying to get other sims needs taken care of, my main sim was able to just saunter in and take care of the newborn after about 15 minutes of not being able to make her go in without teleporting. Again, this seemingly happens every time she gets back from work, and weirdly never after she visits another lot.
