Images and media missing/corrupt in Storyline 2

I've been working on a course for 6 months now, and the client recently decided to split it in two. I split it, and then had to copy over one scene to the other "half" after I had split it. Unfortunately several images, 2 videos, and 2 audio files became wonky. They might show in the preview panel on the left - but not on screen or in published file. I tried to do a "change picture" but it would not do a direct change picture from the same source file - UNLESS I changed the name of the source file. Strangely, the audio that corrupted still showed that there was audio on the timeline, but no bar appeared to control it - just the label "audio 4".  I'm going to be working on this file for a couple more months now and CANNOT keep redoing weeks' worth of fixes if it corrupts or has some weird memory cache issue again. I tried everything - tried created a new storyline file and importing the scene from the good "original" file. I tried copying over the scenes in question again in new file. The only thing that worked was finding the source file - renaming it - and doing a change picture. The video and audio that was MIA had to be deleted and reinserted again.  Help!