Hi @grayarea
Thanks for the bug report. I can’t replicate the issue on my end, but it sounds like another plugin / theme code is conflicting with ACF when saving fields.
Can you check the DB for the new entries in the wp_posts table and check if the fields are saving with the post_type of ‘acf-field’ or ‘acf-field-group’.
It sounds like the child field’s are being modified to ‘acf-field-group’ by another plugin. Perhaps one that effects the page order?