Found my problem :) in ap mode, go to network, LAN, and set adress type to Static IP. The c3150 thought approx. Every 10-15s there is no dhcp server, activated his dhcp server and reconnected every...

Same problem here. C3150 V2 FW2.1.0.0.9.1 Multiple times per minute reconnecting on 2.4G and 5G. I dont know why. The device is running in ap mode btw.