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of course, but help me a bit, which repo is most relevant for this issue ? core or src ?

On deployments with multiple gateways, opting for automatic firewall rule creation via "Register rule" or "Pass" creates rules that do not include the advanced mode "Reply-to:" configured, so if a query comes via GW1 it will probably return via GW0 and be dropped.
Solution is to set to manual and enter your desired reply-to gateway in the dropdown.
Hope this helps