If you’re using a seo plugin (e.g. yoast) and some custom filters to modify the meta titles/descriptions, make sure, that you are not using get_field() there or at least only on fields, that have really been created with acf. I didn’t get any notice from the acf plugin on one of my website, but then I realized all my meta data is broken, because the placeholder values are no longer working; switching to get_post_meta() fixed all issues in this case also
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