Random bitmap-based symbols turn red when I reopen files

This happens repeatedly. Not all symbols but random ones involving bitmaps where I've made edits, like overlapping certain sections to alter the image using the lasoo and copy tools.

Error message: "could not load scene into memory. Your document may be damaged."

Red screen: https://i.paste.pics/7065398b5665d121997bfb7f1edfaa7d.png 

I have several complicated backgrounds that I need to recreate all over again. I can't keep doing this. Any ideas on why it's happening. 

Updating Animate and engaging hardware acceleration did nothing.