table-headline-line disappear in mobile version

Hey verena_1992,
I believe that this maybe do to your Enfold theme & WordPress & PHP is very old:
WordPress v4.8.5 (wordpress is now at v4.9.1)
Enfold v4.0.7 (enfold is now at v4.2.1)
PHP Version v5.5.38 (wordpress recommends php v7)

I recommend creating a staging site and migrating a copy of your site to it to test how updating these 3 will effect your site.
You can create a staging site on your webhost in a sub-domain or you can use a localhost on your computer.
a good migration tool is all-in-one-wp-migration
All-in-One WP Migration tutorial
If you don’t feel comfortable doing this, perhaps hiring a freelancer to assist would be in order.
At minimum, please create a full backup, I recommend https://wordpress.org/plugins/duplicator/
Hope this helps.

Best regards,
Mike

Hi,
I belief I found a solution, I added this to your quick css:

@media only screen and (max-width: 767px) { 
.responsive .avia_responsive_table .avia-data-table tr:first-child th {
    display: block!important; }
.responsive .avia_responsive_table .avia-data-table td:before {
	display:none !important;}
}

Please clear your browser cache and check.

Best regards,
Mike

Hi,
Glad we were able to help, we will close this now. Thank you for using Enfold.

Best regards,
Mike