I've seen this both locally and in ephemeral.   Suspect it has something to do with profiles.
So far I've noticed this with ENABLE_SPLUNK_HEC and UMB_ENABLED.

Locally, if I start the swatch-contracts service with the stage profile, but set UMB_ENABLED to false, I expect not to see the "SRMSG16215: Unable to connect to the broker" log spam.  This isn't the case.

SWATCH_SELF_PSK=placeholder UMB_ENABLED=false QUARKUS_PROFILE=stage ./gradlew :swatch-contracts:quarkusDev

In ephemeral, the default value for ENABLE_SPLUNK_HEC is false, but I'll frequently see error messages referring to the splunk hec url.  With that flag set to false, ephemeral shouldn't even be attempting to reach a splunk url.