Unnecessarily a check / tick mark appearing in my button [ made of anchor tag i.e. link ]

Question

I'm using the following code to display a button to clients:

<table role="presentation" cellspacing="0" cellpadding="0" border="0"
style="border-collapse:collapse; background:#005984; width:auto;">
<tbody>
    <tr style="height: 30px;">
        <td style="height: 30px; padding: 5px 22px;">
            <a class="button-a button-a-primary" href="https://google.in" target="_blank"
                style="font-family: sans-serif; font-size: 15px; line-height: 15px; text-decoration: none; color: #ffffff;">
                Click Here to begin </a>
        </td>
    </tr>
</tbody>
</table>

Note: My application sends mails to clients, hence client opens the mail on multilple devices/browsers. Due to security concerns, No idea as of now, on which environment this issue appearing, will be updated if as I get.

My client is seeing an extra checkmark next to the button:

I cannot reproduce with same html as above. But somehow the client can and has sent me the previous screenshot.