If there are multiple targets that have both the largest size and shortest movement distance, priority is set in clockwise rotation, starting from the 12 position

12 means 12 o'clock, i.e. noon, on a clock. for a distance of 2 this would give the following priorities for the blob S:

            y
    .------------->
    | 14 15 0 1 2
    | 13        3
 x  | 12    S   4
    | 11        5
    v 10  9 8 7 6

I got the same test error as Alan-Turing13.

I agree with him that [8,3,4] should move towards [9,6,3] instead of [5,6,3] because the first goes to the right, the second to the left.

Are there other criteria for the movement that are missing in the description?

Maybe your map still has this entry for c from a previous execution.
I had the same problem with a static map that persisted values after each test.