​@Mikko Knuuttila - Since I cannot see what you are seeing or what is going on with your Free Plan team set up, I will suggest an alternative route where you create a new Business Plan subscription and then move your boards from your free plan team space to your new Business Plan team.

You could do this right away, or I can convert your post into a support ticket and you'll need to wait for a reply from the support team. 

Here is how you can create a new subscription:

https://community.miro.com/ask-the-community-45/issues-upgrading-my-plan-18859?postid=69546#post69546

And then steps on moving boards:

https://help.miro.com/hc/en-us/articles/360017730093-How-to-move-a-board

And if there are boards that are in your free plan team that you do not own, but want copies of, you can duplicate them and move the duplicates:

https://help.miro.com/hc/en-us/articles/360017730113-How-to-duplicate-a-board

Let us know how you make out!