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After some more trial and error it appears to be a theme conflict. I am using the same theme (with some alterations) on another site where batch renaming works fine, so I’m going to look for the culprit.
Sorry to have bothered you, I’ll post my solution here if I find it.
I think I found it. In my functions.php I had added this function:
add_action( 'pre_get_posts', 'items_unlimited_list');
function items_unlimited_list($query){
$query->set( 'posts_per_page', '-1' );
};
When I removed it, batch renaming worked as intended.
Hope this helps anyone encountering this issue.