jQuery how to fix Cannot set property '_DT_CellIndex' of undefined?

From your code, I don't see the DataTabe initialization, usually placed inside the Document Ready function. So:

• Try to Initialize your table with an explicit configuration for each column ("visible:true" is a dummy setting that just confirms it is visible)
• Add the "datatable" class to your table html. Example:

Example:

$(document).ready(function () {
var myTable= $('#tablebqup').DataTable({
    columns:[
    //"dummy" configuration
        { visible: true }, //col 1
        { visible: true }, //col 2
        { visible: true }, //col 3
        { visible: true }, //col 4
        { visible: true }, //col 5
        { visible: true }, //col 6 
        { visible: true }, //col 7
        { visible: true }  //col 8 
        ]
    });
});

And on the html:

<table id="tablebqup" class="tableau table datatable table-fixed table-bordered table-dark table-hover ">

Explanation:

The "DataTable" initialization method should have the same number of columns on its configuration as the number of <th>'s/<td>'s on your html.

Wrong example:

 //Javascript Code
 var myTable= $('#myTableId').DataTable({
    columns: [
        //any column configuration
        { "bSearchable": false }, //col 1
        { "bSearchable": true },  //col 2
        { "bSearchable": true },  //col 3
        { "bSearchable": false }, //col 4
        { "bSearchable": false }, //col 5
        { "bSearchable": false } //col 6 
    ]
});

And the html markup:

<table id="myTable" class="table datatable">
<thead>
    <tr>
        <th>col 1 header</th>
        <th>col 2 header</th>
        <th>col 3 header</th>
        <th>col 4 header</th>
    </tr>
</thead>
<tbody>
    <tr>
        <td> data col 1, row 1</td>
        <td> data col 2, row 1</td>
        <td> data col 3, row 1</td>
        <td> data col 4, row 1</td>
    </tr>
</tbody>
</table>

So even if the number of <td>'s and <tr>'s are matching on the html, having more columns configured on the DataTable method will cause this exception to be thrown. In this example, removing the configuration lines for col 5 and col 6 from the DataTable method would fix the error.

It gives me this error when the number of td doesnt match the number of th, or when I use colspan...

Depending on your css, it could be hard to see. I'd add a border to the table while testing it out...

A simple mistake, the table header had a column " with no title, but the column did not exist in the table itself. I could not see it missing (because o no title and no borders).

Was helped by looking at the line in the datatable.js which gave the error - was implying a tr was at fault, so looked more carefully at my table and not my overall code