Here's my code:

<!-- Main Table -->
        <table background="pink">
            <tr>
                <td style="width: 50%; padding: 0px;">
                    <!-- Left Table -->
                    <table background="yellow">
                        <tr>
                            <td>[[Company Logo]]</td>
                        </tr>
                        <tr>
                            <td>[[Company Address]]</td>
                        </tr>
                    </table>
                </td>
                <td style="width: 50%; padding: 0px;">
                    <!-- Right Table -->
                    <table background="lightblue">
                        <tr>
                            <td class="bold">Loan Number:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_loan}</td>
                        </tr>
                        <tr>
                            <td class="bold">Amount Due:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_remaining_payment}</td>
                        </tr>
                        <tr>
                            <td class="bold">Date Due:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_date}</td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>

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^ Result is as expected But when I add longer text to any of my <td>'s... the whole thing get's shifted and is no longer 50% of the screen....

Added Text:

<!-- Main Table -->
        <table background="pink">
            <tr>
                <td style="width: 50%; padding: 0px;">
                    <!-- Left Table -->
                    <table background="yellow">
                        <tr>
                            <td>[[Company Logo]] !!!ADDING SOME MORE TEXT HERE TO SHOW THAT THIS GROWS ALOT!!!</td>
                        </tr>
                        <tr>
                            <td>[[Company Address]]</td>
                        </tr>
                    </table>
                </td>
                <td style="width: 50%; padding: 0px;">
                    <!-- Right Table -->
                    <table background="lightblue">
                        <tr>
                            <td class="bold">Loan Number:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_loan}</td>
                        </tr>
                        <tr>
                            <td class="bold">Amount Due:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_remaining_payment}</td>
                        </tr>
                        <tr>
                            <td class="bold">Date Due:</td>
                            <td class="right-aligned">${record.custrecord_da_stmt_date}</td>
                        </tr>
                    </table>
                </td>
            </tr>
        </table>

New Result:

Solved with a real hacky workaround: You can add a <tr> with a line height of 0, and 2 <td>'s with some placeholder text That forces the whole table to stay at 50%

<!-- Main Table -->
<table background="pink">
    <tr>
        <td style="width: 50%; padding: 0px;">
            <!-- Left Table -->
            <table background="yellow">
                <tr>
                    <td>[[Company Logo]] !!!ADDING SOME MORE TEXT HERE TO SHOW THAT THIS GROWS ALOT!!!</td>
                </tr>
                <tr>
                    <td>[[Company Address]]</td>
                </tr>
            </table>
        </td>
        <td style="width: 50%; padding: 0px;">
            <!-- Right Table -->
            <table background="lightblue">
                <tr>
                    <td class="bold">Loan Number:</td>
                    <td class="right-aligned">${record.custrecord_da_stmt_loan}</td>
                </tr>
                <tr>
                    <td class="bold">Amount Due:</td>
                    <td class="right-aligned">${record.custrecord_da_stmt_remaining_payment}</td>
                </tr>
                <tr>
                    <td class="bold">Date Due:</td>
                    <td class="right-aligned">${record.custrecord_da_stmt_date}</td>
                </tr>
            </table>
        </td>
    </tr>
    <tr name="table-fix" style="line-height:0;">
        <td style="height: 0; width:50%;">
            <p>
                <#list 1..500 as _>
                    &nbsp;
                </#list>
            </p>
        </td>
        <td style="height: 0; width:50%;">
            <p>
                <#list 1..500 as _>
                    &nbsp;
                </#list>
            </p>
        </td>
    </tr>
</table>

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