I noticed that it usually happens at the same point of the file transfer (28% for some files, 47% for others).
What seems to be happening is that after some amount of data is transferred (or transfer time), the network adapter on the remote host where the client VPN is running simply stops working making the internet connection drop, and then it drops the VPN connection as well.
That's why I believe it's an issue with the remote client and not the MX.
After some time it gets back online.
I tried virtually everything already and it simply keeps happening with multiple laptops (not sure if all because most people don't transfer large files through the VPN link).
Here is a list of what I remember having tried:
- Uninstalling all security software
- Disabling Windows firewall
- Restarting internet modem
- Using a VPN from another firewall connected to the same modem as our main firewall
- Changing network profile (Public vs Private)
- Changing file type (exe vs dummy file)
- Changing MTU
- Changing from Wireless to Wired
- Copying using shared drives, RDP (copy from RDP and paste locally), RDP local drive configuration, and robocopy/
- Disabling "Allow the computer to turn off this device to save power" on the network adapter