Symbol Not Listed In Library

I have a symbol 'Woman 2 Walk Right' whch is in use twice in my project. The symbol is fully operational.

But the symbol name has disappeared from the list in the library so the only way I can re-use it again is to copy a previous instance and paste it.

I am very organised with my library items - well named folders, sub-flolders and everything in order. I have looked through all the folders more than once but 'Woman 2 Walk Right' is nowhere to be found.

I have tried duplicating the symbol on the stage by right-clicking and selecting 'Duplicate Symbol' which is then named 'Woman 2 Walk Right Copy' but that doesn't appear in the library either.

Where can it be?