Custom attributes values are mostly not imported even if correctly mapped.
Install import extension - Create different kind of attributes (integers, text selector, boolean …) -
Create a csv file with headers value = field name or title - and lines = accepted values - map every attribute while importing
Only one attribute is correctly imported and all others are ignored. It seems that this attribute is the only one which is not depending of any category.
All attributes linked to the chosen category of import should be imported
Note that on the import mapping form, some attributes not corresponding to the chosen import category are asked to be mapped