Logic Masters Deutschland e.V.

This is my second exploration of the queendom idea. This is mainly an anti-knight sudoku but with a twist. If you have tried my last queendom sudoku, the rules here will be slightly different. For example, the queens will not necessary satisfy the anti-queen constraint (I hope you will see why). Also I have replaced the term "well-guarded" with "uniformly-guarded" (pun intended!). There is also a little mystery to solve, which can be resolved by first solving the sudoku.
Rules about sudoku:
In the magical queendom, the sixth 3x3 square (coloured grey) is a magic square. There are queens represented by the number 5. Four of them have been located and labelled ABCD clockwise. Every other queen cannot be a knight's move away from the labelled queens.

There are vikings who want to attack the queen represented by 1s and 9s (two are given below and are coloured green). A queen is "under-attack" if at least one edge-adjacent cell is a viking.

There are knights from regiments 2,3,4,6,7 and 8. No two knights from the same regiment can be a knight's move apart.
To clarify, each of the numbers 2,3,4,6,7 and 8 have the anti-knight constraint.
Each of the four labelled queens are "uniformly-guarded". That is, for each labelled queen its four edge-adjacent cells (coloured blue) are all knights from different regiments.

Description of mystery:
Harmony has been lost in the magical queendom with at least one queen under-attack by vikings. This is all due to one of the labelled queens. As detective to this case, your task is to find the conniving queen. Solving the sudoku will provide evidence to incriminate that queen. If you need help in tracing this queen, write a hidden comment to your fellow detective.

You can solve this case on Penpa-Edit. Have fun detective!

Hint about mystery:
Think about why the anti-queen constraint fails. Which queen turns out to be attacking another queen (a queen's move away from each other)?

Hint about knights:
Think about the structure of the 8 knights surrounding a pair of queens (which are a knight's move apart, eg queens A and B). Think about the four knights in the middle, and the four knights on the outside. Remember that there are exactly 6 regiments in total (2, 3, 4, 6, 7 and 8).

Hint about magic square:
What can you say about the central cell of a magic square? Which character is it?
What can you say about the corner cells of a magic square? Which characters are they?
If you are unfamiliar with the properties of a magic square, write a comment and I will explain them to you.