From someone who posted on the other site
Thank you for contacting Wizards of the Coast Customer Service! The issue with the Mastery Pass not granting Uncommon ICRs on Levels 70 and higher has been reported to the Arena development team. Players who are missing Uncommon ICRs will be receiving a grant sometime in the near future. Thank you for your patience while this is being worked on.
You’re supposed to get uncommon icrs for each level above max. It’s obviously not a huge deal, but it’s still vault progress.