Traffic inside namespace / operator

Hi

A pretty basic question. We are running Istio (on openshift)
I have configured a namespace to use istio and it works on one of the application there.

The other application uses infinispan (operator) and need to communicate with infinispan to start up.
When ServiceMesh is enabled in the namespace it will not start up. Infinispan does not have the sidecar. If I remove it from the mesh it starts up fine.

So I wonder, how is Istio interfering with that traffic ? Is there any good articles / videos about how this kind of traffic works in Istio?

Thanks.