I can confirm that these UIs are working as expected and there’s no active bug here (related the above discussions about staff limits, change plans page or Starter).
After the ^change to deprioritise Starter on the pricing page was made last month, we made it a legacy plan earlier this month so it will not appear as an upgrade option going forward. We were making multiple experiments at the same time, so apologies for any confusion. In hindsight, we should have announced the change at the time it was made.
About the Change Plans page, yes it was briefly introduced for a while but it has been removed as we want to redesign it in the future. For info about your hosted plan or making changes, Admin > Manage Account continues to be the correct page is the correct place to find all the information about your hosted plan or make changes to it.