el-table 合并单元格为何部分成功，部分失败？

<el-table :data="waterData" border :span-method="handleSpanM">
  <!-- 前4列固定 -->
  <el-table-column width="65"><template slot-scope="scope">{{scope.row.name }}</template></el-table-column>
  <el-table-column width="70" label="系数">
    <template slot-scope="scope"><el-input size="mini" v-model="scope.row.factor"></el-input></template>
  </el-table-column>
  <el-table-column width="120" label="等级分数">
    <template slot-scope="scope"><el-input size="mini" v-model="scope.row.grade"></el-input></template>
  </el-table-column>
  <el-table-column width="180" label="符号选择">
    <template slot-scope="scope"><div class="symbol"><span style="display: none;">{{ scope.row.symbol }}</span><span class="symbol_range"></span></div></template>
  </el-table-column>

  <!-- 后6列可编辑，列头也需要设置成可编辑的 -->
  <el-table-column v-for="(column,index) in 6" :key="`column-${index}`" width="120">
    <template slot="header"><div><el-input size="small" v-model="waterForm[`water${index + 1}_label`]"></el-input>  </div>  </template>
    <template slot-scope="scope"><div><el-input size="small" v-model="waterForm[`water${index + 1}_factor`]"></el-input></div> </template></el-table-column>
</el-table>

merge(tableData) {
  // 要合并的数组的方法
  this.companyArr = [];
  this.companyPos = 0;
  this.simpleArr = [];
  this.simplePos = 0;
  this.symbolArr = [];
  this.symbolPos = 0;
  for (var i = 0; i < tableData.length; i++) {
    if (i === 0) {
      // 第一行必须存在
      this.companyArr.push(1);
      this.companyPos = 0;
      this.simpleArr.push(1);
      this.simplePos = 0;
      this.symbolArr.push(1);
      this.symbolPos = 0;
    } else {
      // 第一列
      if (tableData[i].name === tableData[i - 1].name) {
        this.companyArr[this.companyPos] += 1;
        this.companyArr.push(0);
      } else {
        this.companyArr.push(1);
        this.companyPos = i;
      }

      // 第二列
      if (
        tableData[i].name === tableData[i - 1].name &&
        tableData[i].factor === tableData[i - 1].factor
      ) {
        this.simpleArr[this.simplePos] += 1;
        this.simpleArr.push(0);
      } else {
        this.simpleArr.push(1);
        this.simplePos = i;
      }

      // 第四列
      if (
        tableData[i].name === tableData[i - 1].name &&
        tableData[i].factor === tableData[i - 1].factor &&
        tableData[i].symbol === tableData[i - 1].symbol
      ) {
        this.symbolArr[this.symbolPos] += 1;
        this.symbolArr.push(0);
      } else {
        this.symbolArr.push(1);
        this.symbolPos = i;
      }
    }
  }
},
// 合并行
arraySpanMethod({ row, column, rowIndex, columnIndex }) {
  if (columnIndex === 0) {
    // 合并第一列
    const _row_1 = this.companyArr[rowIndex];
    const _col_1 = _row_1 > 0 ? 1 : 0; // 如果被合并了_row=0则它这个列需要取消
    return {
      rowspan: _row_1,
      colspan: _col_1,
    };
  } else if (columnIndex === 1) {
    // 合并第二列
    const _row_2 = this.simpleArr[rowIndex];
    const _col_2 = _row_2 > 0 ? 1 : 0;
    return {
      rowspan: _row_2,
      colspan: _col_2,
    };
  } else if (columnIndex === 3) {
    // 合并第四列
    const _row_3 = this.symbolArr[rowIndex];
    const _col_3 = _row_3 > 0 ? 1 : 0;
    return {
      rowspan: _row_3,
      colspan: _col_3,
    };
  }
}

// data
waterForm: {
  water1_label: "前10分钟",
  water2_label: "前20分钟",
  water3_label: "前30分钟",
  water4_label: "前40分钟",
  water5_label: "前50分钟",
  water6_label: "前60分钟",
},