Yes, I just encountered this and found this post.
In the article at https://macaddress.io/faq/how-to-recognise-a-docker-container-by-its-mac-address an algorithm for mac address generation is described.
I guess it can return duplicated MacAddresses sometimes? Perhaps it can happen occasionally when starting up several containers simultaneously. For me the consequence was that sometimes some containers could not ping each other within the docker network (SDN).
Quite annoying if this is the case, there should be some uniqueness checks for this?