Post thumbnail import stops at #705

Hello,

I am trying to import 1700 posts (CPT) with a custom tax and custom fields. The import stops importing the images at #705 out of 1700 on the three runs I have tried. The rest of the data is imported successfully. In the uploads folder there are several 0-byte JPG files also which seems a bit odd.

Any idea what could be tripping this limit or the 0-byte images? I have increased max execution time to 3600 and the script completes successfully.