Game wrong in saying I have no room for new sim

As I was completing a task that required a sim to give birth, I was prevented from finishing it by the game insisting that the household was full, despite only 3 sims being present. The max is 4 sims so this should not be an issue. Coupled with the fact that I have exactly 1 more space available for said new sim,  I'm left very baffled and annoyed. Please help. I have reset the game and phone and nothing has changed