@AndreCasarin 

If you had Deco E4 with 100Mbps Ethernet port, that would be expected outcome. Deco M4R has gigabit Ethernet ports and what you describe would be unusual for it.

Deco E4 is very similarly looking to Deco M4R, and people occasionally confuse them. Check Update Deco screen in Deco app (More/System/Update Deco), it'll confirm what Deco model you have. Here is an example of that screen:

@Alexandre. 

Just checked model, please see below.

This is what I've checked, M4R has gigabit, however doesn't work :(

The only thing that I didn't try yet is to switch which one is Main, but not confidente.

Thanks in advance

André

  @AndreCasarin 

It is M4R. In Deco Access Point mode it should definitely deliver more than 100Mbps on a wired backhaul.

Try the clean test that may help to narrow where the problem is:

Configure Deco to run in Access Point mode;

Connect device with gigabit Ethernet port, such as laptop, to Main Deco with short Ethernet cable, verify speed test on laptop reports 300Mbps;

Unplug laptop, plug Satellite Deco to that same short Ethernet cable connecting to Main Deco. Power Satellite M4 on and verify it reports Ethernet backhaul in Deco app;

Take another short Ethernet cable, plug to second port of Satellite Deco and to laptop. Run speed test on laptop again.

  @Alexandre. 

Ok, got it

I will try and let you know, let's see

Thanks

André