Good morning friends,

A query please, I have the main router RouterBOARD 962UiGS-5HacT2HnT, this connects to a second device RouterBOARD wsAP 5Hac2nD-US, the connection is from port 5 of the main router (PoE) to the input port of the second router.

I already have like this, more than a week, I have the following problem:
The speed of the second rouerter (wsAP) when I test it via ethenet is only 90 Mbps. But the main router has a speed of 170 Mbps. Does anyone know why this happens?

wsAP ac lite only has 100 Mbit/s Ethernet ports, so add to it the overhead of PPPoE encapsulation and you've got the answer.

If possible, please POST the Config of both Device
(/export hide-sensitive file=anynameyouwish)

Guess Op didnt check specs for ethernet?
Of course for $49 one should be thinking why so cheap! (and this is reflected by both the ethernet and wifi chipsets included)
What rocks my socks is the marketing which fails to make this clear and you have to really search for it.
They do however BOAST about both 2.4 and 5ghz WIFI capabilities.

They do state 300Mbps 2.4 and 433Mbps 5ghz (for the famous marketing ploy of AC750 ).
In reality speeds will be real world more likely 300/3= 100Mbps for 2.4 so that matches the ethernet throughput, reasonable!
433/3 = 144 Mpbs which will not be realized as ethernet limited to the internet which is unfortunate but not too much of a loss
So in conclusion, the ethernet 10/100 kinda matches the wifi capability of the router.