This is an older question but I thought I’d chime in with what I believe was the issue here and this question ranks high in the searches.
In a multi-site situation where you’re hardcoding the fields via PHP you need to make sure those options are being initialized on all the sub sites as well. If you have a global options page on the primary site within a Multisite network but those options aren’t also initialized on the sub sites, you’ll get the above behavior. Specifically the data for the field is accessible but it doesn’t bring in any of the ACF-specific formatting. For example, a repeater field will just return the number of sub-items, not the actual content of the sub-items.
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