Hi, the arena chest opening is visual only and the rewards displayed there have already been added to all players when the arena rankings reset at 8:00 UTC. The arena chest pop up may not appear or only appear after restarting the game.

Have you checked your inventory for new Divine artifacts? Everyone gets the rewards and there is no bug in delivering those, only in the delay of receiving the chest pop up.

Regarding the ancient shard, it's possible that you have opened some shards just as the ranking reset occurred and you may have also opened the reward ancient along with other shards.