@Sangello 

Do you see these devices in Deco app and do they show as connected with Ethernet?

@Alexandre. Yes they're shown connected with ethernet. Even though i download/upload large files it still shows 0/0.

  @Sangello 

If they are shown as connected by Ethernet, everything is fine. 

This is known issue. At least, I know it for all three years I own Deco mesh. Once, I was running full PC image backup to NAS, with close to 800Mbps traffic flowing steadily through Satellite Deco to which PC is wired, for hours. Deco app did show 0 for PC bandwidth during all that time. 

In the info page of Deco unit you will see an aggregated bandwidth usage for that Deco. For some reason, this value is more reliable and updated better than for individual devices.

I decided to ignore bandwidth usage for devices reported in Deco app. I like Deco mesh in general, such minor issues are forgivable. 

  @Alexandre. As you stated i checked the individual Deco unit's info page, i can see the aggregated bandwidth usage now. It's interesting why TP-Link didn't fix it for three years, i hope it will be fixed on the next update. Thank you so much clarifiying everything Alexandre.

Hi, with the latest update (1.2.0) this issue has been solved. Deco now shows both download and upload bandwidth traffic.