Wifi keeps dropping

Replacing my 2 Airport Extreme APs & 1 Airport Express (one on each floor) The GND floor Airport Extreme was connected a SKY router. I relaced all the Airport fit with the Orbi router RBR50 and Sat RBS50 - set the Orbi router to AP Mode. I started to notice the network dropping, when I checked the logs on the SKY router its network port dropped the link - when I checked the log on Orbi the log was a new one. Also noticed when a new device is connected the wifi goes off-line. 

Any ideas why the network keeps dropping?