I can't 100% see what your trying to do or what is happening, but in my experience items often disappear when doing stuff like this in EA (copy, paste, renaming), I think it's EAs problem with tracking stuff in the background files.
Do you have all the assets in the new document? Have you tried exporting (right click save to file) and then importing (the '+') all the symbols before copying across the layers and animation - this may be more robust. Also locked layers don't copy (for me), notice some of yours are locked.
Just use duplicate instead.
Interesting points – cheers for the heads up about locked layers (even though that's doesn't seem to be what's causing it). I've since started a new document and I'm not having the problem now. So, mysteriously solved for now.
Hi resdesign. I appreciate you taking the time to answer, but you've really been no help. You haven't stated any context or explanation.