Ok here are fixes step by step and we’re applying this fix on the next version update too.
Open template-tags.php file go to line 191 and find the code below :
_x( 'Published on %s', 'post date', 'pure-and-simple' )
replace it with
__( 'Published on %s', 'pure-and-simple' )
open content-single.php file and find this below code on line 46
_e( 'Last Modified on ', 'my-text-domain' );
and replace it with :
_e( 'Last Modified on ', 'pure-and-simple' );
go to footer.php file and find the below code in line 35 :
esc_attr_e('All rights reserved.', 'preferential')
and replace it with
esc_attr_e('All rights reserved.', 'pure-and-simple')
I hope it helps.