I cannot recreate the error.
If you can do some debugging for me.
Open the file /advanced-custom-fields-pro/pro/fields/class-acf-field-repeater.php
just before line 412 add
echo '<!-- ';var_dump($i);var_dump($sub_field);var_dump($sub_value);echo ' -->';
Load the page, look at the page source just before the error and tell me what appears in the comment added to the page.
