Unfortunately I was unable to find an answer in the similar threads, so here I am...

Basically the issue is that TL-PA7017P (Gigabit Ethernet) is offering even slower speed than TL-PA4010P (100Mbs Ethernet).

I have purchased a starter kit of TL-PA4010P powerline adapters. They offer 600Mbs powerline / 100Mbs Ethernet speed. I have been using them for a couple weeks for my other devices that do not need much bandwidth but require stable connection.

In the meantime I have tested it (TL-PA4010P) with my main PC and I was amazed - it was exceeding 95Mbs speed on speedtest.net and was very stable. Therefore I have decided to order faster adapters for my main PC, as the WiFi connection is very unstable.

I have purchased another kit - TL-PA7017P kit (which offers 1000Mbs powerline / 1Gbs Ethernet) and I have connected it the same way as before:

1. one PA7017P connected directly to the router (with the provided cat. 5e cable)

2. second PA7017P connected to my main PC (with the provided cat. 5e cable)

3. one PA4010P connected to another device on another circuit (with the provided cat. 5 cable)

All devices are paired. The issue is that TL-PA7017P connected to my main PC is getting only 87-89Mbs, whereas it should offer 1Gbs... It is even slower than the PA4010P I have tested in the same configuration. The same power outlets, no new power appliances in the network. All environment is the same...

Any clues to why is PA7017P not even exceeding 100Mbs? Is that 3rd adapter (PA4010P) slowing the whole network down perhaps?

Speedtest.net:

This is how it looks in the TP-Link App: 

https://imgur.com/xiHIIFR https://imgur.com/xiHIIFR