[PS] Can't go up or down floors

Hello, I was having the same issue last week.  I spent a lot of time working on the problem.  I am a builder and have been working on this house for years.  And this problem is new. Anyway, I saved all of my rooms in the house in case I needed to do a demolition.  The thing that fixed the problem was adding additional walls in my 2nd floor.  It used to be a long corridor.  Now there are segments of corridor with archways.  It actually looks good like this.  I was routing sims from different spots of the wide open 2nd floor (after removing rooms), and they were walking the perimeter and avoiding walking in the middle of the big area. They would also use the balcony to navigate from one room to another, rather than walking in the middle of the 2nd floor space.  There is definitely a problem.