I discussed this at length before & thought we had it solved here. But this was using a CSVi 6 RC version.
I am now using 6.4.2 in a new site, I have the exact same template set up & confirmed the settings.
I also am testing with the exact same CSV import file.
In the above/previous post, we had it working so that you import the file, with the product information and multi-variant information twice, rather than import once, then goto available fields, before importing for a second time.
I am assuming that the ability to just import twice has now somehow been removed, as after importing the file for the second time I get an warning saying
"These fields have been found but are not supported by CSVI:
Size. Either these fields do not exist in your system, or the list of available fields need to be updated. To update the list of available fields go to Available Fields and click on Update."
Although I have also tested ,but importing the file, then going to update the available fields and the new field does not appear, so I have attached the import file & logs to see if there is a problem or if I have missed something.
Thanks
Andy