Hi,
We recently redid the way Traefik handles configuration flags, which includes the way an entrypoint and its parameters are specified.
https://docs.traefik.io/v2.0/routing/entrypoints/#configuration
As you have figured out, you were previously using the syntax that was in effect before that change, and you found the new syntax to do it properly now, so it's all good.
As an aside note, in the future please try to use specific versions of the official Traefik image (e.g.: traefik:2.0.0-alpha7), instead of using the experimental one, as it makes things much harder to debug and reproduce otherwise.