Deco M5 units are not connecting via wire

I have three Deco M5 units, the main unit is set as router connected to the internet. The other two units are connected to the main unit via switch (I also tried without switch). My issue is that the secondary units are not connecting it via ethernet, see this screenshot: – which is surprising as the third unit connects to the second via ethernet correctly. I also took the photo of the setup (please don't judge me for the messy cables), by the LED lights you can see the switch has connected to all three Decos correctly. Can you tell what I may have setup wrong?

Question by Vojtěch on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.