[EDIT] We have now sent the missing rewards to the players who completed Season 3 prior to the issue being resolved. Thank you again for your patience while this issue was fixed, and our apologies for any inconvenience caused by this.
[EDIT] We have now resolved the issue with Season 3 Completion loot. Players completing Season 3 should now recieve the correct loot. We are investigating how to resolve this issue for the players who have already completed and claimed the Mission Reward prior to this being fixed. Thank you for your continued patience.

-Removed mention of Stage completion rewards for clarity as it is unrelated to this issue.-
There is currently a known issue with the Mission Rewards for completing Season 3. We are investigating the issue here and hope to get it resolved as soon as possible.

We will update here when we have more information. Thank you for your patience and our apologies for the inconvenience.