I set up my Deco M4 with 3 Deco's. First with Wifi, it all works well.

Then I connect them wired. One over a TP link switch, the other over a Netgear switch as well.

Ziggorouter (NoDHCP) - Deco1 (DHCP) 192.168.50.1 - TPlink switch - Deco2 192.168.50.100

                                                                                      - TPlink switch - Netgear switch - Deco3 192.168.50.103

cable check has been done by a Network cable tester. 
 

The wired connected Deco's are blinking red and gets a warning in the app.

BUT they work well in wired mode. I can see that with the speed check, 250 Mbps down in stead of 53 Mbpsat the same place with de Deco3 powered off.

How to solve the red leds?

there is no other DHCP server in the network.