WEBDAV poor transfer rate with Nextcloud 12 and an NGINX PROXY

Hi all,

I have a problem when i use webdav on a synology NAS or Windows Client (native or with NAVDrive) the transfer rate never exceed 1.5MB/s ; i have a dedicated server with 500mbps guaranteed.

I have a VM for NGINX PROXY (small VM)
I have a VM only for Nextcloud (NGINX/PHP/REDIS/MariaDB)

I think the problem is between vm proxy and vm nextcloud, when i forward port 80/443 directly to VM Nextcloud, transfer rate is better.

Do you have an idea ?