There are a couple of causes for a repeater field returning the number of rows instead of an array.
The first is that ACF doesn’t know what post ID to use to get the field, but I don’t think this is the case. It would only be the case if the field key reference was missing in the database. Since you are getting the number of rows, then you are getting something, so also an indicator that this is not the problem. However, this could also happen if ACF does not know the ID of the post in some cases depending on other fields and what it thinks the post ID is. Supplying the correct post ID when like
get_field('field-name', $post_id) would resolve this.
The second thing that could cause this is that there is a filter or action somewhere that is interfering with the queries that ACF needs to do to get the repeater. I suspect this is more likely the issue. With recent changes to WP, there could be a change, but you’ve already tried the standard deactivate plugins and switch themes. However, are you still using and/or code that generates the PDF? If not then I’d try removing that and create a different output and see if you’re still only getting the number of rows.
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