i tried ingesting a folder with many images and some subfolders . After it was done i noticed that in some subfolders many images are missing. 

I tried rerunning a fast and a deep sync. Now even more images are missing. 

The images are located on a NAS. When i copy one of the subfolders that has missing images to another place on the NAS , and just ingest this folder, all images are ingested. 

What can this be - how can i debug this?