This has been a persistent, ongoing bug that the devs have yet to acknowledge. I’ve been documenting this and almost all other competitive bugs since season 34 here:
Please spread the word.
To Apotzen: Every competitive season since around Season 18 of Overwatch 1 has allowed diamond players to be on the leaderboards, including Seasons 1 and 2 of Overwatch 2. The only exception to this is the final season of Overwatch 1, Season 36, in which all diamond players were removed from the leaderboards and were denied all Top 500 rewards. I have created a comprehensive post regarding this and almost all other competitive bugs since Season 34 linked above. Please respond to this thread with your own issues and create your own posts so that I can add them to the list and hopefully we can get these issues resolved.
This is just so incredibly and painfully frustrating. Not only did I not receive my Top 500 icon from competitive CTF this season, but the career profile stats also removed the proof of me hitting Top 500 in open queue in Season 36 as well. We need to make our voices heard and make the devs give us the rewards we earned.