After disabling and enabling the phase 2 on one end, the tunnel came up.
It was not possible to ping through the tunnel but it looks like the routing works.
I then checked the ipsec firewall roules but they were ok (IPv4 * * * * * * none). I also added such rules on the lan interface on both ends.
Still, the ip is not pingable.
EDIT:
After adding an outbound NAT rule and switching to hybrid mode, I can finally reach through the tunnel.
Adding a third phase 2 shows the red arrow again on this phase 2. Re-enabling it does not help, even after a few times.
The ipsec log shows the phase 2 as if it was connected:
charon: 10[CFG] received stroke: add connection 'con1002'
Jul 7 22:29:48 charon: 10[CFG] added child to existing configuration 'con1000'
Jul 7 22:29:48 charon: 07[CFG] received stroke: route 'con1002'
Jul 7 22:29:48 ipsec_starter[35735]: 'con1002' routed
But the red arrow on the status page stays and the tunnel is not connected in fact.