lineageos 17.1 no incoming

[Chris]

I'm running the f-droid repo of the wireguard client on lineageos 17.1
After the tunnel is up:
I can ping the wireguard client, and I can initiate an outgoing connection 
through the tunnel.

However, a process binding on all interfaces will not see any incoming traffic 
on tun0.
The same process works fine with incoming traffic on wlan0.

Sending the TCP SYN from the wireguard server through the tunnel, never receives 
an ACK.

Openvpn does not show this behaviour.

As the tun0 interface successfully reacts to pings, I guess it may be an 
iptables problem.
I.e. the traffic on tun0 is differently firewalled than the traffic on wlan0.

Chris