Hello again,
I have opened a case at the same time with extreme TAC. he advised to enable debug logs following the 2 commands:
configure log filter defaultFilter add events nl severity debug-verbose
enable log debug-mode
Once I have done that, I started to see the reason why it is failing.
Authentication failed for Network Login 802.1x user host/xxxxx Mac xxxxxxx port 1
Client[1, xxxxxxx] auth move result: Destination VLAN not supplied
Client[1, xxxxxxx] authVlans preprocessing result; Destination VLAN not supplied
802.1X received authentication result 1 for client xxxxxxxxx from AAA
An EAP packet was sent to RADIUS for client xxxxxxxx via AAA
I understood that the switch is expecting the destination vlan from the radius server. I configured it and now it works properly.
I may have wrongly understood the document, however the destination vlan part is put in the additional notes on the documentation, as if it was optional.