I’m having the same issue. For some reason the field returned is not acting like a true Array. If I do echo get_field(‘user_name’) I get all of the values separated by a comma. If I do echo count($user_field) it shows 11 values.
However, when I try to pull out an array value I can’t get it to work. I’ve tried a bunch of stuff. I’m totally stuck and I can’t find any documentation on ACF about it.