Did you ever open Deepin Store?
At the first startup of Deepin Store your computer will move to best mirror available.
Try it.

It's definitely a problem for me. I've used Deepin Store, and it doesn't seem to have made any improvement. I have a 30 Mb connection which can download things at around 3MB/second. The best I've gotten from a Deepin repository is around 50KB. It's hard to wait 10 minutes for a 30MB file, when everything else comes in 60 times as fast. I'm a user in the US with > 25yrs experience using Linux. (I can remember constructing Xwindows modelines by hand)

I share the same experience and sometime the when trying to download a software via deepin store a message saying "waiting for download" but actually nothing happen. Deepin os is great but the devs behind it need to address these issues and try to overcome them if they want to increase Deepin popularity.

Maybe that's because their CDN does not cover the whole world.
At least the speed is good for me and in many parts of China.
You may choose a mirror at https://www.deepin.org/mirror.html

I realized I now after the installation completed 1. item - changed the mirror and everything went successfully!
For example http://ftp.fau.de/deepin/  the speed at 1.2 MB sec! And everyone forgot about the problems with the update!

But why do people say to open Deepin Store if Deepin Store doesn't help at all???!!! Deepin store is dead slow too! It's almost impossible to install anything via Deepin Store, so why giving this advice is beyond me!