iOS App on External network sends a /api/webhook/.... with encrypted data. No response received

[etamminga]

iOS device model, version and app version Model Name: iPhone 11 Software Version: 16.6 App version: 2023.4 (2023.460)

*Home Assistant Core Version Home Assistant 2023.8.1 Supervisor 2023.07.1 Operating System 10.4 Frontend 20230802.0 - latest

Up until somewhere in 2023.1-3 I had no issues. iOS App running on the internal WLAN just fine. Using HA local authentication and reaching the server using http://internal-ip:8123. External access worked as well, using a Fortigate firewall that terminates the TLS/SSL session and forwards the request to home assistant. https://my-public-fqdn:8123 -> http://internal-ip:8123. Using LoadBalancer/Virtual server technology.

Since a few months (haven't had time to determine which version caused this) the external access stopped working. Internal access still works fine.

I have done extensive troubleshooting on this and am not able to determine the cause. My last finding comes from a wireshark capture made on the internal network of the external session. The iOS app sends an /api/webhook/... with an encrypted body which is NOT answered by HA. Meanwhile other http requests succeed just fine. Nothing visible on the iOS app in the meanwhile. When doing a pull on the App (swipe down) the hamburger menu appears, without any content/options.

What is going on? How can I troubleshoot this any further. Asked in Forum as well, without any constructive response.

I'd rather have this working again as it is the cleanest way of terminating my session on my own network.

I have wireshark captures available and am willing to test anything requested.

Regards, Erik