It may be hard to see from my screenshots, but the Nurse and Merchant are sitting on the same chair. Despite the Nurse being visible from a distance, only the Merchant can be interacted with. The 1st screenshot has housing info (the Nurse lives on the floor below), and the other 2 have what it looks like from a distance and up close. The problem is on the bottom screen, sorry for my shoddy screenshotting. Strangely, the only time I can remember the Nurse in her room properly is during a solar eclipse. Also, this problem never happened prehard mode, just some random point preplantera.