"Import external media library attachments" not importing

Yesterday I decided to start hosting everything with 1 cdn instead of amazon and photon, now some of my posts have external images, not too worried about the old ones now but I have added about 6 posts today so far, some with external images and none are being imported.

Is the import a purely manual feature, as the last time I tried it it imported everything, including items that were already in my library, instead of only external items which is what makes sense, so not keen on running it again. Host attachments is also enabled.

Not really sure what to do, googles not helping and the documentation on this feature leaves a lot to the imagination.

https://www.ads-software.com/extend/plugins/w3-total-cache/