Strange UTC showing up on site

I’m using your free and premium plugins.
When WP Simple Booking Calendar is activated, UTC is losing time. ( Correctly, 8hours added to them.)

I can reproduce this issue on the default wp theme with no other plugins.
I also have the same issue on the server of the different provider.

When I comment the follow lines out in the plugin, UTC becomes normal.

if(get_option(‘timezone_string’)){
@date_default_timezone_set(get_option(‘timezone_string’));
}
if(get_option(‘gmt_offset’)){
@date_default_timezone_set(wpsbc_tz_offset_to_name(get_option(‘gmt_offset’)));
}

if you have any solutions to this problem I will be glad to hear them.

Thank you!