Plain HTML is rendered in Gmail app email [closed]

I using rails and letter opener to view how my emails look. When I paste the HTML content in litmus to see the behaviour of different clients, in gmail app alone I am able to see some plain html getting rendered. Something like

<td align="center" style="font-size: 0px; word-break: break-word

In all other clients, I am not able to find this issue. I even tried app.getresponse.com to send emails. The same issue is occurring my mobile's gmail app. What might me be the issue? I have tried html validator. My HTML content is correct