Audio File randomly disappeared

I’m currently backing up all my Cubase files on to an external SD when I came across a project that I’m currently working on and noticed one of the audio files was missing. I haven’t backed up this project yet, and the folder that contains this audio file hasn’t moved. I’m easily able to find the missing file, but even when I find the file and tell Cubase this is the missing file, it doesn’t show up when I open the project.