This often happens to me, since I like to work with unions.
When it happens, all it really takes is me closing and re-opening studio. After that the problem is usually solved. You might want to try doing this.
Another thing I suggest doing is to try and possibly union a random brick with it. This could possibly have the union reload, and make it visible.
If that doesn’t work, I suggest doing what others said.
- Trying to put it into a new game
- Saving a local copy, and trying to see if it’s in that
- Go back on an old save
The cat looks amazing by the way. I hope one of these solutions work in a PAWS-itive way.