OpenVPN client not working in VLAN

renpen

Good day,
I have a client (VM running on ESXI,ubuntu 20.04) connected to a L3 Switch which adds VLAN Tags to the traffic. In my case that specific client is in VLAN 12 and got the IP 192.168.12.2. The Switch is connected to a SG3100. Routing and Firewall happens on the SG3100 as my network is not that big.
I have configured the VLAN as a separate interface on the SG3100 and I can connect to my other devices in the other VLANS as well as the internet:
Rules VLAN 12
Mainly I allowed all traffic. I'm just setting up my Homelab so right now, everything is open. I will restrict it more in the future ;)

Running an OpenVPN client on the machine 192.168.12.2 does not work. The complete machine hangs at

Sat Oct 31 10:52:35 2020 /sbin/ip link set dev tun0 up mtu 1500
Sat Oct 31 10:52:35 2020 /sbin/ip addr add dev tun0 local 10.32.0.238 peer 10.32.0.237
Sat Oct 31 10:52:37 2020 /sbin/ip route add 89.187.165.53/32 via 192.168.12.1
Sat Oct 31 10:52:37 2020 /sbin/ip route add 0.0.0.0/1 via 10.32.0.237
Sat Oct 31 10:52:37 2020 /sbin/ip route add 128.0.0.0/1 via 10.32.0.237

If I open a separate session executing top before executing the openvpn connection, then top freezes when I start the openvpn connection. Additionally, I can not open another session after the openvpn connection started.
CTRL + C takes a lot of time to take effect in the session where I started the openvpn connection. After the program is closed, top is not frozen anymore and I can open new sessions. So very strange behaviour ... .

I was wondering about this issue, as I can connect to the same VPN via other clients e.g. my Macbook. Out of curiosity, I switched the NIC on my ESXI host for this VM and therefore making the VM part of VLAN 1. Then the openvpn connection works without issues, hence my assumption that the issue is somehow connected to the VLAN setup.
However, I have mainly the same firewall rules defined in LAN:
Rules LAN

Do you have any idea what can cause this issue? I'm pretty sure that I missed something with the VLAN setup, but I can not imagine what that might be ... .

Best,
René