I am so confused on what I just did

So I was making a score of a song I had made and I was changing the dynamics of one of the parts. Everything was fine until I went to go do the same to another part and mezzo-forte just didn't exist anymore. Like there's just a blank space. I'm so confused because this is the first time I've seen something just straight up disappear (other than my scores when the system crashes). Like its not even in the "More" section.