Sharepint Document Upload Problem for Zip File with less than 50MB size

Today I got an issue ticket from a customer that he got an error message:

Virus Found

"Toolkit.zip" contains the following virus: "Exceedingly compressed size; Tagged ID: 20726101_24E4_46C5_838B_94F2CD5A2F5D" .
This file cannot be saved to the document library. If you want to save this file to the document library, clean the file using alternative virus scanning software and try saving it again.

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But the customer means that the file is 100% without virus and its file size is less than 50MB.

Our document library polics for allowed file size is 50MB, but the file is a zip file with less than 50MB. It seems it should pass the polics. The problem should be caused by scaning virus, because the zipped file is being unzipped during scaning. I upzipped the file and found the file size is 56MB, more than 50MB. I tried to upload another file with original file size 53MB and the zipped file size is 42MB andgot the same error information. Well, the problem is caused by the zip file size...

The upload allowed file size is unzipped file size...