Unread Flexible fields can't be saved

Hey guys,

I’m creating my own WordPress theme with the use of flexible content.
After I’ve managed the fields on the edit page and click the button to upload it, the fields disappear.

I’ve used the code below in the template file.
The file name of the template file is : page.

<?php if( have_rows('content') ):
while ( have_rows('content') ) : the_row();
if( get_row_layout() == 'imageRight' ): ?>
<h3><?php the_sub_field('contentTitle'); ?></h3>
<div class="content imageRight">
<?php the_sub_field('contentText'); ?>
<img src="<?php the_sub_field('contentImage'); ?>">
</div>
<?php elseif( get_row_layout() == 'imageRight' ): ?>
<h3><?php the_sub_field('contentTitle'); ?></h3>
<div class="content imageRight">
<?php the_sub_field('contentText'); ?>
<img src="<?php the_sub_field('contentImage'); ?>">
</div>
<?php endif;
endwhile;
endif;?>

Does anyone know what the problem is? Please, let me know.
Thanks in advance!