PR2100 to Dropbox very slowly

Good morning, I started a data backup from Dropbox app on NAS WD PR2100 to my dropbox plus account.
Data uploading (about 90gb) is very slow compared to my upload internet speed.
From speedtest I have an upstream of 3mbit/s, but network monitor shows a dropbox upload under 50kilobit/s. Nothing else use internet connection.
Dropbox said the problem is the app installed on the NAS because it is an app created by WD.
Could you help me to increase the speed?

Thank you very much.

Hi,

You could refer to the following link: Network: Common Causes and Solutions for Slow Data Transfer Speeds