[bmwlover]

I am using the latest version of 7zip. The file arrives directly on my NAS and I check the MD5 hash directly after downloading without further manipulation. I will try again to see if I still get the same MD5 hash and report back.

I use "My JDownloader" directly connected to my NAS with a 1gb/s fiber connection.

jdownloader is known to corrupt things. 

use the official mega client

I had same problem 1 time and it was hdd problem.