Using UE4 4.25, may vary for older versions
I had this same problem and I just fixed it all in one day. I figured out if you removed the “corrupted” or unreadable file from your project in your file explorer, you can go to Your Project/Saved/Backup → find the unreadable file’s saved data (In this case the map and the Build Data), copy and paste into your content browser folder and rename them respectively (This is what I did at least and it worked). I know I’m about 2 years too late, but at least I can help others who are trying to solve this issue in the future.
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