It would seem to indicate an issue with the Radius server but it is not clear from this whether the issue is between your concentrator and the Radius server or if it is between the client and the Radius server. Are there other clients that connect to this concentrator and authenticate with that Radius server? If so do they work? Is the problem isolated to this client or are other clients similarly impacted?
I would suggest getting in touch with the administrators of the Radius server and asking their assistance in resolving this, beginning with whether they are seeing error messages in their logs that correspond to this attempt to authenticate.
It seems to me that I have seen symptoms similar to this when the node secret got out of synch between the concentrator and the Radius server. It might be worthwhile requesting that the administrator of the Radius server clear the node secret (generate a new node secret for your machine) and for you to delete the file from your concentrator and have it relearn the node secret.
We have configured the outside and inside Interface with official ipv6 adresses, set a default route on outside Interface to our router, we also have definied a rule , which also gets hits, to permit tcp from inside Interface to any6.
In Syslog I also se...