Help: Long audio file now stops after a certain point in the timeline?

I have a really long audio file (I'm helping a friend edit something) that was working fine last time I opened it. When I opened it this morning, it stops at hour 5 (5:15 to be exact) and now has this diagonal lined portion followed by blank audio that goes on till the end of the track (which you can see in the screenshot).

I've removed the cache and renamed the files but it's still showing up like that.

These edits took a while... am I doomed?

Thanks and Happy Holidays to whoever has read this!