You could be running int an ACF caching issue, I’ve had trouble with it in the past while working on plugins. When you get a field group ACF sets a cache value. Once this is done you basically can’t alter he field group, well you can, but nothing happens. After you get a value you sometimes need to clear a cache before you can make modifications to te field group you need to clear that cahce.
YOu’ll need to did around in the ACF code to figure out that cache value you need to clear.
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