Hi there,
I just tried reproducing your issue locally to test a theory about might what be causing the discrepancy. I was unable to trigger the behavior you mentioned using the docker-compose you provided and building the latest https://github.com/hwdsl2/docker-ipsec-vpn-server from source. Can you confirm you are also running commit c282440? If that’s correct, are you able to provision a second device to test if something specific to the device is not working as expected?
Please let us know!