Poor openvpn perfomance


i have an Odroid N2 with the latest 9.2.2 version of CE. I’m using Zomboided VPN Manager for OpenVPN kodi plugin to connect to an offsite Synology DS415+ NAS trough OVPN to access my tvheadend server and some video content like my ripped BD collection.

The file access/copy speed is very slow, about 2-3MB/s trough VPN, though i can achieve much more throughput on https webdav, cca 30Mbit which means it maxes out my internet connections max downloads speed (300/75 Mbit/s fiber internet).

I checked the CPU and RAM usage when i copied files through vpn+nfs /vpn+smb and it was negliable.

Could you please tell me, how i can improve speed of the VPN on the Odroid? I had a 6th gen Celeron NUC which could max out my internet conn download speed with Libreelec and same plugin.

I use the same settings as before (AES-256-CBC)

I always use (inside and outside the home) CoreELEC clients connected to the main server also CoreELEC through zerotier VPN. The maximum connection speeds are 30-50 Mbps and I have no problem.

Years ago, before learning about CoreELEC, I used OpenVPN to connect to my home from the outside using an RT-AC87U router server and the speeds were 30 Mbps.

In summary, in VPN connections I have always seen speeds of 30 Mbps or 3-4 MB/s. This seems normal to me.

P.S. My internet connections exceed 300 Mbps. I have also seen that the file transfer speed between devices connected to zerotier VPN and to the same home network reaches 160 Mbps.