I'm converting the c routine below into mainly ASM code, can anyone see what I might have done wrong when translating it to ASM?

PLAIN C VERSION
void plexSort() {
    char nxt_idx;
    char nxt_y;
    char s;
    char sortedIDX;
    char m;

    for(char m: 0..PLEX_COUNT-2) {
        nxt_idx = PLEX_SORTED_IDX[m+1];
        nxt_y = PLEX_YPOS[nxt_idx];

        sortedIDX = PLEX_SORTED_IDX[m];

        if(nxt_y < PLEX_YPOS[sortedIDX]) {
            //Shift values until we encounter a value smaller than nxt_y
            s = m;
            while (true) {
                PLEX_SORTED_IDX[s+1] = PLEX_SORTED_IDX[s];
                s--;
                sortedIDX = PLEX_SORTED_IDX[s];

                if (s == 0xff) {break;}
                if (nxt_y >= PLEX_YPOS[sortedIDX]) {break;}
            }
            // store the mark at the found position
            s++;
            PLEX_SORTED_IDX[s] = nxt_idx;
        }
    }
    //Prepare for showing the sprites
    plex_show_idx = 0;
    plex_sprite_idx = 0;
    plex_sprite_msb = 1;
    plex_sprite_mask = 0xff^plex_sprite_msb;

    plexFreePrepare();
}
-------------------------------------------------------------------
ASSEMBLY CODE VERSION...

void plexSort() {
  char nxt_idx;
  char nxt_y;
  char s;
  char sortedIDX;
  char m;

  asm {
    lda #0
    sta m
  !forLoop:
    // nxt_idx = PLEX_SORTED_IDX[m+1];
    lda m
    clc
    adc #1
    tax
    lda PLEX_SORTED_IDX,x
    sta nxt_idx

    // nxt_y = PLEX_YPOS[nxt_idx];
    tax
    lda PLEX_YPOS,x
    sta nxt_y

    // sortedIDX = PLEX_SORTED_IDX[m];
    ldx m
    lda PLEX_SORTED_IDX,x
    sta sortedIDX

    // if nxt_y >= PLEX_YPOS[sortedIDX]; if true, skip while loop
    tax
    lda nxt_y
    cmp PLEX_YPOS,x
    bcs !whileEnd+ // skip while loop

    // Shift values until we encounter a value smaller than nxt_y
    //            s = m;
    lda m
    sta s

  !whileLoop:
    // PLEX_SORTED_IDX[s+1] = PLEX_SORTED_IDX[s];
    lda s
    tay
    clc
    adc #1
    tax
    lda PLEX_SORTED_IDX,y
    sta PLEX_SORTED_IDX,x
    // s--;
    dec s

    // sortedIDX = PLEX_SORTED_IDX[s]
    ldx s
    lda PLEX_SORTED_IDX,x
    sta sortedIDX

    // if (s == 0xff) {break;}
    txa
    cmp #$ff
    beq !whileEnd+

    // if (nxt_y >= PLEX_YPOS[sortedIDX]) {break;}
    ldx sortedIDX
    lda nxt_y
    cmp PLEX_YPOS,x
    bcs !whileEnd+ // >= exit loop
    jmp !whileLoop-
  !whileEnd:
    // end of while loop
    // store the mark at the found position
    // s++;
    inc s

    // PLEX_SORTED_IDX[s] = nxt_idx;
    ldx s
    lda nxt_idx
    sta PLEX_SORTED_IDX,x

    // loop if m <= PLEX_COUNT - 2
    inc m
    lda m
    cmp #PLEX_COUNT-1
    beq !+
    // not finished for loop yet...
    jmp !forLoop-
  !:
  }

  // Prepare for showing the sprites
  plex_show_idx = 0;
  plex_sprite_idx = 0;
  plex_sprite_msb = 1;
  plex_sprite_mask = 0xff^plex_sprite_msb;

  plexFreePrepare();
}