I found the reason - just letting other in same situation know the solution:
It is not enough for the custom application to call vpnapi.detach() - the process has to be terminated.
Cisco AnyConnect VPN Client GUI exiting, version 2.5.1025 , return code 100003 [0x000186A3] indicates that another process that has connected to vpnapi.dll is still running. Regardless of the other process has called vpnapi.detach()
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...