Table headers overlapping on second page when printing/PDF

Question

Stuck on this little issue where the table headers are overlapping the tbody rows as below;

This is the generalized code that creates the table;

<table id="symptoms" class="table table-bordered  mg-t-15" style="table-layout: fixed;">
                    <thead>
                        <tr class='bg-gray-300 tx-12 tx-uppercase tx-color-02'>
                            <th>Symptom</th>
                            <th>Status</th>
                            <th>Rating</th>
                            <th>Frequency/Details</th>
                        </tr>
                    </thead>
                    <tbody class='tx-12 mg-t-10'>
                            <?php foreach ($this->patient->medical->symptoms as $symptom): ?>
                                <tr class='tx-12'>
                                    <td>....</td>
                                    <td>....</td>
                                    <td>....</td>
                                    <td>....</td>
                                </tr>
                            <?php endforeach; ?>
                    </tbody>
                </table>

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I have tried a range of suggestions from SO that all haven't worked so I'm at a bit of a loose end here haha!