Slow Network speed for large file transfers

Hello,

I have a home server running two VMs, Jellyfin and another NextCloud on bridge networking mode. The Host OS is Windows and hypervisor is VMWare.

I wanted to expose both to Internet so deployed a 3rd VM running Ubuntu 20 and then followed the installation instruction to install this software (Nginx Proxy Manager).

Following are some configuration details

Hardware -> Intel Core i7 4790 / 32GB DDR3 / SATA SSD / Gigabit LAN
Host OS -> Windows 11
Hypervisor -> VMWare 16

Router -> 192.168.1.1 (having the public IP)
Ports -> 80/443 is forwarded to Nginx VM

Host OS -> 192.168.1.25
VM-Jellyfin -> 192.168.1.60
VM-NextCloud -> 192.168.1.30
VM-Nginx -> 192.168.1.45

Nginx Host added as subdomain-jellyfin.mydomain.com -> goes to jellyfin and similar 2nd subdomain for nextcloud too.

Setup works. Both these VMs (Jellyfin / NextCloud) are accessible from outside internet via their respective subdomains.

However large file transfers are really really slow when going via this Reverse proxy VM. For example, both NextCloud or Jellyfin VMs are unable to sustain more than 15-20 megabits. The transfer (upload or download) starts fine with my connections max speed, but gradually within few seconds, it starts to slow down and settle at around 15-16 megabits / sec.

Just to compare, if I cut the middle proxy VM by directly exposing the Jellyfin or Nextcloud VMs to the internet via router port forwarding, both of them are able to run at full speed of my connection (250 megabits / sec). Be it upload or download.

Since this Proxy Manager is web UI based, so chance of me messing up anything is slim. I have not enabled SSL in any of my VMs. I have not added any extra or advance config argument to the proxy manager UI.

So what should I do now to troubleshoot this performance issue?

Thanks in advance.

Start with the reported comparison between direct port forwarding and traffic through the Nginx Proxy Manager VM. Review the proxy VM, VMware networking, and Nginx Proxy Manager configuration while reproducing large uploads and downloads. Done means identifying a specific bottleneck or configuration cause for the drop from 250 to roughly 15–20 megabits/sec.