This happens if you are missing subsequent parts (002, 003, etc.) or if one of the parts is corrupted.
The .7z.001 extension is a split 7-Zip file. Unlike a regular .7z file, which is a single compressed archive, a split archive requires (001, 002, etc.) to be present in the same directory to function. Key Facts: Format: 7z (7-Zip compressed).
This article explains what these files are and how to properly extract them. What is a .7z.001 File?
