If I try to import more then 100 hundred listings with each having 10 or more images as attachments the import process runs a long time which is understandable but cuts of the import showing no reason, error (because there were no errors) and just does not finish importing it all.
My listings have quite a lot of selectable custom attributes also which maybe adds on complexity of the import process making it slow and potentially causing some time out in the import function in controller class.