"Auto-detect" option for gateway breaks my outbound connection

[Apollo13]

Hey guys,

a few months ago I wrote a post (https://forum.opnsense.org/index.php?topic=11314.0) about how setting the "auto-detect" option for the gateway on WAN interface breaks my outbound connection on OPNSense 18.7. Back then I got no response/help but thought this problem will be fixed in newer versions. Unfortunately it is still present on 19.1.

The situation in short: My OPNSense has a public WAN IP (e.g. 100.0.0.100) and I created a "gateway" entry (e.g. for IP 100.0.0.1), which I marked as "default". As soon as I select "auto-detect" on my WAN interface the attached clients on LAN are unable to reach any external system. Switching to gateway "100.0.0.1" restores the capabilities.
The OPNSense itself is able to access (ping) all hosts regardless of the concrete selection.

Can anybody help? Thanks in advance.

[mimugmail]

When you set auto-detect .. do you have some auto rules in Firewall : NAT : Outbound?