Garageband deleting audio file data?

While editing my podcast yesterday, I received this notification 3 times, all while doing very regular actions. I've been working on this episode for over a month now, and this is the first time this has happened. As you can see, the audio files in the bottom tracks have been wiped of their data/content. There is no sound or data in the clips anymore, rendering it useless. (Luckily, I was able to use an old exported version of the episode, but it meant I couldn't edit each host's audio separately.) I'm terrified that this might happen when editing a new episode, and we will lose our audio clips entirely. Any idea why this happened and how to prevent it in the future?