Hi jardindanslavallee ,
Your problem doesn't seem the same because you're using a third-party plugin that can be causing the incompatibility.
You can try deactivating it and check if the problem is still there, and if not, you can try to use it in conjunction with the ATUM "Decimals in Stock Quantity" setting. Maybe it will work, but I can't ensure this.
Best Regards,
José Andrés