OpenVPN low download speed (700KB/s) vs upload (5MB/s)

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Hi!

I have a very strange problem with download speed form server inside virtual private network.

The point is to have a private network with two machines, for now, only accessible via OpenVPN.
I have everything setup (virtual machines, pfSense 2.6.0, OpenVPN) and everything connects and works except for the very slow download speed of 700KB/s from the Ubuntu machine to My PC. Upload speed is normal, higher than 5MB/s.

As you can see in the diagram, everything takes place inside the main network, wired connection only! So we can exclude the ISP and bad wireless connections.

I did some test and i don't know what to make of them:

1. When downloading from Ubuntu to W10, inside the virtual private network, everything is OK
2. When downloading from W10 to My PC through VPN, everything is OK.
3. If i connect the Ubuntu machine to the Bridge virtual switch directly, everything is OK.
4. I even connected with SSH+SCP to the pfSense machine through VPN and everything is OK.
5. Uploading and downloading to My PC from Ubuntu through VPN gives the same results using SAMBA file share or SSH+SCP.

It does not appear to be the ubuntu machine, as it works perfectly when connected to directly.
It does not appear to be the VPN machine because it works with different machines.

I tried changing the MTU from default 1500 to 1492 and 1400...no change.
pfSense is updated to 2.6.0, OpenVPN packages are updated to 1.6.8
Ping and traceroute give good results 1-2 ms.
All connections are IP based, so we can exclude any DNS problems.
System/Advanced/Networking/ Disable hardware checksum offload is checked.

If you are think network loop, all NAT is disabled.

I think the problem is between the vpn tunnel network 10.3.8.0 and the private network 172.19.10.0 but it somehow only affects Ubuntu..

Any thoughts?

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This post is deleted!

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In my attempt to debug the network issue i ran netstat -see on the ubuntu server before and after download test. Keep in mind that i don't actually know what they mean or how to fix them but this is the values that popped out:
TCPSackRecovery: 1107
TCPLostRetransmit: 927
Fast retransmits 4410
Retransmits in slow start 402
TCPTimeouts: 403
TCPLossProbes: 808
TCPSackRecoveryFail: 402
TCPSackMerged: 332
TCPSackShiftFallback: 1120

The entire network is virtual and there cannot be a problem of congestion so, again, it was a dead end. This morning i made a backup of the configuration and installed pfsense development version daily snapshot 2.7.0 from 06.01.2023 and.....it worked!

I still don't know the cause but i think i can run the development version until the stable one comes out.