I had this happen in career mode. The path was really long and the first exhibit was really far away from the entrance. The guests would just turn around at the ticket booths. I tried adding some guest facilities halfway but they still wouldn't come in. At that point, I had to step away from my computer for a bit cause of food so I quit the game and when I came back it worked fine. Even without the guest facilities which didn't autosave before I quit. The guests were happy to come in after a restart.