Error after order submit

[raduenea]

Hello,

I have Presta 1724 installed on php 7.1.

I add some products in my cart, complete delivery etc, and submit the order. 

Insted showing Thank You page it's show me html code like bellow: 

<div style="width: 100%; height: auto; margin-top: 0px; font-family: 'Arial', Georgia, serif;"> <table style="height: 73px; width: 100%;"> <tbody> <tr style="height: 18px;"> <td style="width: 50%; height: 73px;" rowspan="4"><img src="https://plafarcoral.ro/img/cms/presta.jpg" alt="" width="76" height="100" /></td> <td style="width: 50%; height: 19px; text-align: right;" colspan="2"><strong>Factura</strong></td> </tr> <tr style="height: 18px;"> <td style="width:

Print screen attached for entire page. 

Went well in the last 2 years but suddenly appear this. I really don't know how to fix this.

Please help me.

Thank you.