Reset to factory defaults did not work either. In the controller it is shown available, but adoption fails.

  @MarioRuck 

I seem to remember that the firmware requires some new ports, do you have a local controller or is it remote? Which ports have you opened to the controller?

You need this port to be opened to controller

  @MR.S 

Thanks for the feedback! I use a local controller based on Ubuntu with ufw disabeld. So I think all ports can be forwarded in the local network. The EAP is shown available at the 

devices - Adopt fails. Are there any logs on the controller, which I can check why the EAP is not taking the takover commands?

  @MarioRuck 

ok, I use ubuntu controller too, I also have EAP653 which works without problems, is the controller installed directly on ubuntu or are you using some container stuff.

  @MR.S 

I run a Ubuntu-VM with the controller on Proxmox, no LXC. All other EAP are still on 1.1.3 and are still working. I defered any further updates on the EAP.

  @MarioRuck 

ok, i'm pretty sure there are some ports you're missing, like i said i had something similar on a firmware a while ago.

try checking that you have all the ports available on the controller.

https://support.omadanetworks.com/nordic/document/13090/

  @MR.S 

Thanks for the update! I checked the open ports from my desktop

NSE: Loaded 156 scripts for scanning.
NSE: Script Pre-scanning.
Initiating NSE at 18:39
Completed NSE at 18:39, 0.00s elapsed
Initiating NSE at 18:39
Completed NSE at 18:39, 0.00s elapsed
Initiating NSE at 18:39
Completed NSE at 18:39, 0.00s elapsed
Initiating ARP Ping Scan at 18:39
Scanning 192.168.126.142 [1 port]
Completed ARP Ping Scan at 18:39, 0.03s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 18:39
Completed Parallel DNS resolution of 1 host. at 18:39, 0.00s elapsed
Initiating SYN Stealth Scan at 18:39
Scanning 192.168.126.142 [65535 ports]
Discovered open port 22/tcp on 192.168.126.142
Discovered open port 8043/tcp on 192.168.126.142
Discovered open port 29817/tcp on 192.168.126.142
Discovered open port 29811/tcp on 192.168.126.142
Discovered open port 29813/tcp on 192.168.126.142
Discovered open port 29816/tcp on 192.168.126.142
Discovered open port 29812/tcp on 192.168.126.142
Discovered open port 29815/tcp on 192.168.126.142

Guess this is fine and not the issue. Are there any logfiles that I can check? I think there are changes in the behavior that are not working well with my old settings before controller version 6.

  @MarioRuck 

You miss TCP/29814

  @MarioRuck 

If you want log goto global and settings, then goto export data, then export running log,

look in server.log