Thanks for the info. Maybe it has something to do with the activated tab for the installation of Portainer after enabling omv-extras.
Because when you have a look on this side you can see the enabled Portainer docker (it's in green) even you haven't installed docker. Maybe this is the issue?
And after installation of docker the system won't install portainer.
I had the same issue. By installing portainer manually (via CLI) it was working like it should