I also started seeing macvlan traces with 6.12.x, however i followed the advice in another thread to disable bridging for the nic running the dedicated Docker network and that seems to have resolved my traces.
Right now the first post in this thread suggests enabling bridging, as i understand this has no benefits when the network is only used for Docker containers and disabling seems to have resolved my macvlan issues, so i think the suggestion should be to disable it.