Premiere Pro beta corrupts my files

I'm working on a big project, shot on Black Magic Pocket Cinema 6K.

I had to use Premiere Pro Beta so I could use the raw video files.

Now the project has become big, for some reason, some files start to go corrupt. Mostly audio files, that when I open my project, the audio doesn't work anymore -- the original WAV files suddenly are corrupted and can't be played in VLC player. I have renders where they still played.

One of my .BRAW files was corrupted as well: The past couple of weeks it just worked fine, suddenly it was corrupt.

The project is currently on an external HDD because of the file sizes, and I can imagine that to be risky.
But everything works fine.

How can I stop this? It endagers the film I am working on.