two client connections -> crash?

[wireguard at lindenberg.one]

I am trying to configure one client system (Ubuntu 18.04.4 LTS (GNU/Linux 5.3.0-62-generic x86_64)) against two servers. The configuration is very similar:

root at Mailcow:/home/joachim# cat /etc/wireguard/wg0-client.conf
[Interface]
Address = 10.200.200.2/24
PrivateKey = ***
DNS = 8.8.8.8 #10.200.200.1

[Peer]
PublicKey = qn6CTz578gbrYpzYkvV2okoqkIFHKye+mRj4i/I8Sz8=
Endpoint = fire.lindenberg.one:51820
AllowedIPs = 0.0.0.0/0
PersistentKeepalive = 21

root at Mailcow:/home/joachim# cat /etc/wireguard/wg1-client.conf
[Interface]
Address = 10.200.201.2/24
PrivateKey = ***
DNS = 8.8.8.8 #10.200.200.1

[Peer]
PublicKey = QAJANxtuAvdT+HR3fP1I2DXq0Azl0T3jF5s+cW7foSA=
Endpoint = nc.lindenberg.one:51820
AllowedIPs = 0.0.0.0/0
PersistentKeepalive = 21

Wg-quick up wg0-client ist at system startup. Now unfortunately when I do wg-quick up wg1-client the network stack kind of crashes. The command does not terminate, and connectivity on all interfaces is broken.
Is this a configuration issue? Should I change ports to be different? Is there some other issue?
Do I have to define two interfaces or could I have just one with multiple peers? But how could I then specify which tunnel to use?

Any suggestion welcome..
Thanks, Joachim