Been there done that
Try going and revisiting Chantry of Secrets in Bloodtide Coast.
For some reason that usually fixes this issue.
If you got the achievement, but not the reward, try clearing your inbox; it’s possibly stalled in the mail queue. (Wait 15-20 minutes afterward to let the new mail filter through.) If that doesn’t do the trick, contact support; they can help you faster than anyone here on the forums.
Try going and revisiting Chantry of Secrets in Bloodtide Coast.
For some reason that usually fixes this issue.
To the person above inbox was clear, map completion rewards come as separate chests. Thank you for the advice revisiting the chantry, after some intensive trials I figured it out with help from my guild, this should be posted somewhere as a known bug or addressed because the initial impact is very frustrating.
Try going and revisiting Chantry of Secrets in Bloodtide Coast.
For some reason that usually fixes this issue.
This. I had to revisit it to get the rewards for completion.