Updating Magento 2 product attribute, Import Add/Update feature always create a duplicate new item, instead of updating

Question

i'm trying to update a custom product attribute called is_eol, but when i use the system->data transfer->import -> import behavior (add/update), it always created a duplicate item with same sku number.

for example, my csv file looks like:

sku, is_eol abc, eol

where sku:abc is already exist in the catalog.