I wrapped my head around this issue for almost a month and finally found a solution. The issue was the Synology Drive Client being incredibly slow with downloads whene installed on a remote computer.
In my case, using a quickconnect ID resulted in a insanely slow and laggy user experience. Switching to DDNS and portforwarding all the necessary portrs solved my issue with fast response times and downloads and uploads using my connection's full bandwidth.
Here what I did in 3 steps.
STEP 1: Enable DDNS on your Synology Nas.
If you own a Synology Nas, there is no need to subscribe to free DDNS services, as Synology allows to use the domain synology.me for free.
STEP 2: Port Forwarding
You need to open your router's configuration page and port-forward ports 80, 443, 5000, 5001, 6690 for TCP/IP protocol.
STEP 3: Connect to your nas usgin DDNS instead of Quickconnect ID
Open your Synology Drive Client settings, then click on Edit Connection and use your DDNS address in place of your Quickconnect ID.
Thats, it. Hope it works for you as well.
