This runs counter to my experience. Keep in mind, I’ve only been working with FreePBX for about 15 years. so there are still things for me to learn, but this isn’t how any of the systems I’ve ever configured has worked.
I have heard similar problem statements from people running on various VPS and Hosted systems, but that’s not a problem with FreePBX, it’s a problem on the way the VPS reports its interfaces to the system. In those cases, there are “extra-PBX” settings that you need to make in the Ethernet configuration files to tie the interface to the system in a repeatable, non-duplicating way.