Hi r4redu
I see. So please, I have to ask you to deactivate all plugins except the ATUM add-ons and Woocommerce, and check if the problem persists. And also try to change the theme by a standard one (like Storefront). This is to check if there is any incompatibility causing this issue.
If nothing of this works, please I have to ask you to open a private ticket and provide us with your website credentials in order to take a look.
This is the link to open the private ticket: https://stockmanagementlabs.ticksy.com/
Best Regards,
Andrea.