Victor's tunic does not appear to be attached to any achievement despite being locked under some achievement. I can't see how to get it or get it.

The victor's tunic when clicked on to see what achievement you need to do to unlock it instead just redirects you to the achievements page in general, and none of the achievements show it as a reward. I think other people have complained about this and Minecraft thinks it's been resolved, but it hasn't, and is still an issue.