Thanks @tau, I just had a look into your mail data over the past 3 days (since your original post) and it appears all Kingdom Defense mail rewards claimed did add the rewards to your inventory.
But in the meantime, I have let the team know that while there are no longer any issues collecting this mail and those rewards being received, the icons for the rewards are still not displaying.
Now instead of blank mails sometimes my KD mail show rewards from another mail. Its still a visual bug, when I click “Collect” I receive the usual KD rewards.
Update: if I click the KD mail first, its still blank (should be silver/gold medals there). But when I click other mails and then go back to KD mail, it shows the rewards from other mails
