@erynxox That used to happen to me, however only with the sims that I did not follow to high school. I had 3 teen sims in my household the older 2 I didn’t follow to and every time the going to prom popped up it didn’t work even by clicking the travel to prom option. But with the youngest teen I follow to high school 4/5 time and when prom came about Saturday and the prompt popped up it finally worked.
I cannot be for certain that’s the reason but give it a go and see if it works.
Good luck