Extremely slow speeds

[FunkyMonkey]

I have a fairly fresh install of OpenVPN 2.12.0 on a roc-rk3328-cc device (Linux server) running Ubuntu 22. The Linux server has a USB 3.0 HDD connected as storage. I have since moved it to a remote family member's house to use as a remote backup system for my personal files.
When I had the Linux server on my local network (1gb switch), I was able to copy files at roughly 30MB/s from a Windows server 2019 system to the Linux server's hosted storage, which seemed to be a limitation of the crappy drive, but suitable for my needs.
Since I moved it remote, I connected to it with OpenVPN 3.4.0 client from the Windows server, and attempted to run the same file copies I did previously. However I am getting around 1 MB/s now.

Both sites have FiOS gigabit connections.
I ran Speedtest.net at both locations from the individual servers and am getting over 800Mb/s up and down.

The VPN configuration is mostly default. Though I tried some of the settings in this guide: https://community.openvpn.net/openvpn/w ... orks_Linux
And they made no difference whatsoever. Still getting 1MB/s. In the course of my troubleshooting, on both client and server config I tried:

Setting tun-mtu at 1000, 1420, 48000
Setting txqueuelen at 100, 1000, 4000
ncp-disable
fast-io
compress
sndbuf 512000
rcvbuf 512000

I checked CPU usage on the Linux server as well and all of the kworker ovpn crypto processes are using around 5-10% CPU total. Total CPU usage is around 20% during the copy.

There has to be something major I'm overlooking to cause this extreme of a slowdown. Any help would be appreciated.

[FunkyMonkey]

Well I made some progress on this issue, turns out robocopy with the /Z flag was responsible for a decent bit of the slowdown over the VPN for some reason. After trying another robocopy without the /Z flag, I am now copying at around 9MB/s (Same speed as just using a default Windows drag/drop file copy operation in File Explorer through OpenVPN tunnel now).

To be clear once again, before installing OpenVPN, I was using the default Windows File Explorer copy and getting 30MB/s (a limitation of the hard drive's write speed, not the network).

9 is still not nearly as much as the 30 I should be seeing, but it is a start.