I discovered the problem myself….
The Client Beryl at 192.168.8.1 has the original factory LAN settings: 192.168.8.1 for the normal LAN and 192.168.9.1 for the GUEST LAN (both IP’s not modified by me). I did not modify any of these IP’s. But I did modify the LAN IP of the Server Beryl from factory setting 192.168.8.1 to 192.168.9.1 in order to be able to have both Beryls on the same network.
When connected through the VPN tunnel and I access 192.168.9.1 (which is the IP of the Server Beryl) from the Beryl Client at 192.168.8.1, the routing accesses the inactive GUEST LAN instead of the remote Server LAN at 192.168.9.1. When I changed the GUEST LAN IP to 192.168.18.1 (it could be another value far away from 192.168.9.1) the problem disappeared.
If the GUEST LAN IP would be disabled when the Guest LAN is not enabled, I would not have this problem. Perhaps a suggestion: Disable the GUEST LAN IP when the GUEST LAN is not enabled! Otherwise a suggestion for the docs: when the user changes the LAN IP, he should change the GUEST LAN IP as well, even if the GUEST LAN is not active.
Thanks!