Greetings from Plarium!
We have applied a quick hotfix today, fixing the issue with Progress Mission that required Bronze or Silver Medals to be gained specifically for the mission to be completed. The bug has been fixed and Medals of higher Arena Tiers now count towards these Missions appropriately. We have also adjusted the descriptions to avoid confusion. Please note that Medals are not converted as they are in the Great Hall, but are rather counted according to 1:1 logic.