Thanks vor your reply and solution. In my case only the subnet mask was incorrect. After fixing this it still not works.
After enabeling to DHCP again, I got a new IP/Adress for the ANNKE and then it works over VPN as expected.
I got mine last week! Updated it to 5.4.5 as suggested. Everything worked as expected.
There is only one annoying point. When conncted via WIFI I'm not able to get the live-stream over
vpn connection. Neither with my android phone nore with my ipad.
Live stream over VPN and LAN connected works...