This is a late response - but we have just had the same errors happening for data exported out of Omatic which we import to SalesForce Marketing Cloud . Our IT team worked out it was exporting as a CSV but with different "Encoding" standard. So it should be being saved as ANSI but it saves as UNICODE.
The only way around this is to open and re-save the CSV. Althought we use Boomi Dell to automatically transfer our files, so we had Boomi reformat the data while it moves it across to Marketing Cloud. Im about to log a request in the forums to have this changed, or atlesat give us the option of what code to save it as.