We are trying to figure out what is happening. We cannot give you a solution for something we are not able to replicate... I hope you understand this...
If what I suggested above doesn't work, the next thing I would try is to discard any possible conflict with any 3rd party plugin. Please, try to disable all your plugins except WooCommerce and ATUM and try again.
Also, make sure you don't have any errors in your PHP error log. If you need to know how to enable and get this log, please read this article: