VM loses the correct time, and must be rebooted daily

[Knautilus]

Hello everyone.

I'm having a problem with a VirtualBox VM where it repeatedly loses the time. This VM is frequently accessed using Microsoft RDP. If the VM runs for about a day, RDP stops working and gives this error:

"Remote Desktop cannot verify the identity of the remote computer because there is a time or date difference between your computer and the remote computer. Make sure your computer's clock is set to the correct time, and then try connecting again. If the problem occurs again, contact your network administrator or the owner of the remote computer." When I access the VM from the host, the time appears to be set correctly.

The VM must be rebooted to correct the problem. The VM, the VM Host (the host is a domain controller), and the computer accessing via RDP are all part of the same AD domain, and are all set to the same time. I've tried running this VM with the "Hardware clock in UTC time" setting turned on, and turned off.

Group policy has all computers on the domain syncing time from time.windows.com.

Other relevant specs:
VM Host - Windows Server 2016
AMD Ryzen 5, 6 core
64 GB RAM

VM - Windows Server 2016
4 cores assigned
8 GB RAM
VM is connected to a VPN proxy in Europe

Please help me figure out why this is happening so I don't have to reboot the VM so often.

Thanks in advance.