No post in 1.3.0?

There is an extra ) in line 4 of content-single.php
I removed that and all was well again
<?php if ( flat_get_theme_option('single_metadata') != 0 ) ) : ?>
Change to

<?php if ( flat_get_theme_option('single_metadata') != 0 ) : ?>

This worked for me, YMMV

ok, thanks

Please download the latest developer version of this theme: https://www.ads-software.com/themes/flat/developers/
Sorry for the trouble that you encounter.
Jackie