I don’t know too much about GF, but I had a similar problem using an import tool importing to a select field. In my case the problem was that the data being imported had a space after each comma, you might check that. multi select fields are saved the same as checkbox fields but if you’re exploding the values with “,” as the separator and it is actually “, ” then all of your values will have a space at the beginning and this could be why ACF is not seeing them.
