I had that happen just the other day. My sim was writing on the guitar right before she went to work. The next day, I went to finish up the song, and it was gone--no longer in her inventory to finish or name. I tried the usual cleaning of files, checking of CC, etc. I figured the song was just gone at that point, so I had her write another one. Later when I was ready for her to finish the second song, she had two songs in her inventory instead of just the second one. There was no indication as to which was the original one and which was the second, so I just told her to finish one. She was able to name and publish it as usual, and when she completed the second song it worked normally as well. I think there is a glitch going on, but if Ginj's sim has written two already and the second didn't cause the first to reappear like mine did, then it's not something consistent.