WordPress Multisite: Images moved to /sites/1?

I noticed that my older images are no longer getting resolved by WordPress 5.3.4. – the file doesn’t exist on that path and 404 gets returned.

For images that were originally uploaded to

https://www.example.com/wp-content/uploads/myimage-300x300.jpg

WordPress now looks here

https://www.example.com/wp-content/uploads/sites/1/myimage-300x300.jpg

The function I’m using to resolve image path (none works with old images):

https://developer.wordpress.org/reference/functions/get_the_post_thumbnail_url/
<img class="full-size" src="<?php echo get_the_post_thumbnail_url($row['ID'], "medium"); ?>">

https://developer.wordpress.org/reference/functions/the_post_thumbnail/
<?php the_post_thumbnail( 'medium' ); ?>

I’m using WordPress Multisite for several years already and never had this problem. Before, the older images of the used to be directly in wp-content/uploads/ directory.

The change could either be part of a WordPress update or a side effect of the newly installed Elementor plugin.

How to overcome this change?