You're using the latest version of PrestaShop shopping cart however it is operated by an old storage system which is not supported by Store Manager for PrestaShop.
To switch to the new image system, go to the Preferences > Images tab and click the "Move images" button. Depending on how many product images you have, it may take a while to move them all into subdirectories:
Once it's finished, go to the Preferences > Products tab and change the "Activate legacy images compatibility" option at the bottom of the page to "No" to use the new image system:
If the issue remains, please submit a ticket here:
we could check your issue individually and advise you on this regard.
Let us know if you need more assistance.