I had one machine on my entire client's network that could never download a LibreOffice document without it being corrupted.

Turns out it was kaspersky intercepting network calls, and deciding it was a very dangerous piece of file, and it would truncate it completely silently.

After wasting a non-billable afternoon on it, I just disabled the antivirus out of desperation and figured it out.

The solution was to generate a self signed certificate and TLS the connection and prevent the bugger to MITM us.

Since this day, even on a local network with behind a proxies and using a VPN, I still use https for all the services if I'm allowed.