So I have a problem where artwork inside a symbol will disapear.
I have a character. I animate the scene, save etc. Close the file. Next time I open it up, the eyes are missing. But you can see a white square where the symbol is. In fact, the symbol is still there. When you go inside the symbol however, all that's inside is a single blank frame. No matter how many layers or frames was inside it before, there's just a single blank frame.
This doesn't happen often, but when it does, it can set me back an hour or two fixing things, depending on the symbol that it happens to. Currently, it's a set of symbols in a prop that have emptied.
Most likely data-corruption issue. Check your RAM.
If RAM is OK, then get into the habit of saving versions of your file with incremental numbers so that you, hopefully, have backups.
Find an older version of Animate that does not give you such problems and stick with it.
Never just upgrade. Always install separately and never remove a well-working version from your computer to replace it with the 'bestest and newest', because they always introduce horrible new bugs and regressions which take multiple hotfixes to patch.
One such very stable and well-performing version is Flash Pro CS6.
Nick - Character Designer and Animator, Flash user since 1998 Member of the Flanimate Powertools Team - extensions for character animation