Import problem for some images

Hi. I encountered the following problem of importing csv files with the help of feeds: some images are not imported, but if I change at least one character in the image name, then it appears when you re-import it. If I return the previous name and import again, also successfully. I attach a tamper plugin on the image field, which replaces the underscore character with the underscore character. After that, most of the problem pictures were imported, but still not all (although there are also underscores in their names). Can anyone help me? Thank you very much.
Version feeds - 7.x-2.0-beta3.